How to reduce CPU Memory usage?

I am working on upload images application which seems working fine for me. I am uploading 100 images. and when i run this process 4-5 times application crashes out.

This seems to me memory usage issue.. How to reduce that memory. I don't want to my application get crashed.

 btn_Cancel.userInteractionEnabled=NO;
    btn_Share.userInteractionEnabled=NO;
    btn_Back.userInteractionEnabled=NO;
    btn_BackTransp.userInteractionEnabled=NO;
    btn_BareCode.userInteractionEnabled=NO;

    [self integratedLoaderView];



    NSURL *url=[NSURL URLWithString:@"http:/apiurl /"];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0),^{
        NSString *str_EstimateNumber=[NSString stringWithFormat:@"%@",txtFld_FolderName.text];
        NSDateFormatter *formatter=[[NSDateFormatter alloc] init];
        formatter.dateFormat=@"yyyy-MM-dd";
        string=[formatter stringFromDate:[NSDate date]];
        NSString *str_time;
        formatter.dateFormat=@"hh.mm.ss a";
        str_time=[formatter stringFromDate:[NSDate date]];
        NSString *str_AppendString=[NSString stringWithFormat:@"%@ at %@",string,str_time];
        NSInteger str_Counter=[[NSString stringWithFormat:@"%lu",(unsigned long)[delegate.ary_ImageData count]] integerValue];
        NSString *str_Value=[NSString stringWithFormat:@"%ld",(long)str_Counter];
        NSString *str_Username=[NSString stringWithFormat:@"%@/Images",txtFld_SelectedFTP.text];
        abc=0;
        for (int i=0;i<[ary_Tosend count]; i++)
        {

            sleep(0.6);

            abc++;
            if ([str_ConnectionStatus isEqualToString:@"WiFi"])
            {
            }
            if ([str_ConnectionStatus isEqualToString:@"Cellular"])
            {
            }
            if ([str_ConnectionStatus isEqualToString:@"No Connection"])
            {
                btn_Cancel.userInteractionEnabled=YES;
                btn_Share.userInteractionEnabled=YES;
                btn_Back.userInteractionEnabled=YES;
                btn_BackTransp.userInteractionEnabled=YES;
                btn_BareCode.userInteractionEnabled=YES;
                NSString *str_Total=[NSString stringWithFormat:@"%lu",(unsigned long)[ary_Tosend count]];
                NSString *str_Saved=[NSString stringWithFormat:@"%lu",(unsigned long)[delegate.ary_ImageData count]];
                NSInteger total_Count=[str_Total integerValue]-[str_Saved integerValue];

                [self saveInDBWhenConnectionLost:total_Count];

                [self ShowAlertForCheckInternetConnection];
                return ;
            }
            if ([str_ConnectionStatus isEqualToString:@""])
            {
                btn_Cancel.userInteractionEnabled=YES;
                btn_Share.userInteractionEnabled=YES;
                btn_Back.userInteractionEnabled=YES;
                btn_BackTransp.userInteractionEnabled=YES;
                btn_BareCode.userInteractionEnabled=YES;
                NSString *str_Total=[NSString stringWithFormat:@"%lu",(unsigned long)[ary_Tosend count]];
                NSString *str_Saved=[NSString stringWithFormat:@"%lu",(unsigned long)[delegate.ary_ImageData count]];
                NSInteger total_Count=[str_Total integerValue]-[str_Saved integerValue];

                [self saveInDBWhenConnectionLost:total_Count];
                [self ShowAlertForCheckInternetConnection];

                return ;
            }

            NSString *str_fileName;
            str_fileName=[NSString stringWithFormat:@"%@_%@ %i.jpg",str_EstimateNumber,str_AppendString,abc];
            NSDictionary *params=nil;
            NSData *imageToUpload=UIImageJPEGRepresentation([ary_Tosend objectAtIndex:i],0.25);
            NSString *encodedString=[NSString stringWithFormat:@"%@",[imageToUpload base64Encoding]];

            params= @{
                     @"categoryName" :txtFld_Category.text,
                     @"folderName"   :txtFld_FolderName.text,
                     @"fileName"     :str_fileName,
                     @"userName"     :str_Username,
                     @"postedFile"   :encodedString,
                     @"accessToken" :@"Q)4%v59!@lyr"
                     };

            AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
            httpClient.parameterEncoding = AFFormURLParameterEncoding;
            [httpClient registerHTTPOperationClass:[AFJSONRequestOperation class]];
            [httpClient setDefaultHeader:@"Accept" value:@"application/json"];
            NSMutableURLRequest *request=[httpClient requestWithMethod:@"POST"
                                                                  path:@"UploadImages/upload"
                                                            parameters:params];

            NSURLResponse* response=nil;
            NSData *data=[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
            if(data.length)
            {
                NSString *responseString=[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
                NSError *error = nil;
                NSDictionary *JSON = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];

                if(responseString && responseString.length)
                {
                    [delegate.ary_GetUploadedCount addObject:JSON];
                    [self responseUpload:JSON];
                    dispatch_async(dispatch_get_main_queue(),
                                   ^{
                                       if(i < delegate.ary_ImageData. count)
                                       {
                                           [delegate.ary_ImageData removeObjectAtIndex:i];
                                           [delegate.ary_TotalImages removeObjectAtIndex:i];
                                           [ary_DataToConvert removeObjectAtIndex:i];
                                           [ary_DataToConvert1 removeObjectAtIndex:i];

                                           NSUserDefaults *default_AllImg=[NSUserDefaults standardUserDefaults];
                                           [default_AllImg setValue:ary_DataToConvert forKey:@"ImageDetail"];
                                           [default_AllImg synchronize];

                                           NSUserDefaults *default_AllImg1=[NSUserDefaults standardUserDefaults];
                                           [default_AllImg1 setValue:ary_DataToConvert1 forKey:@"ImageData"];
                                           [default_AllImg1 synchronize];
                                       }
                                   });
                }
            }
        }
    });

Please tell me.