Following code will help you to add or delete file from document directory.

-(NSString *)saveFileWithOldName:(NSString*)oldNameStr
{
    NSArray *dirPaths;
    NSString *docsDirs;
    NSString *tempStr2;
    dirPaths = NSSearchPathForDirectoriesInDomains(
                                                   NSDocumentDirectory, NSUserDomainMask, YES);
    docsDirs = [dirPaths objectAtIndex:0];


   docsDirs = [docsDirs stringByAppendingPathComponent:folderrName];

    NSString *tempSoundPath;

    NSString *soundFilePath = [docsDirs
                               stringByAppendingPathComponent:oldNameStr];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:soundFilePath])
    {
        int i = 1;

        NSString *tempStr = [oldNameStr stringByReplacingOccurrencesOfString:@".caf" withString:@""];

        //NSLog(@"saveFileWithOldName:tempStr:%@",tempStr);
        tempStr2 = [tempStr stringByAppendingFormat:@"-%d.caf",i];
        //NSLog(@"saveFileWithOldName:tempStr2:%@",tempStr2);
        tempSoundPath = [docsDirs
                                   stringByAppendingPathComponent:tempStr2];
        //NSLog(@"saveFileWithOldName:tempSoundPath:%@",tempSoundPath);


        while ([fileManager fileExistsAtPath:tempSoundPath])
        {
            i++;
            tempStr2 = [tempStr stringByAppendingFormat:@"-%d.caf",i];
            //NSLog(@"saveFileWithOldName:tempStr2:%@",tempStr2);
            tempSoundPath = [docsDirs
                             stringByAppendingPathComponent:tempStr2];
            //NSLog(@"saveFileWithOldName:tempSoundPath:%@",tempSoundPath);
        }

        // rename File
        [fileManager moveItemAtPath:[docsDirs                    stringByAppendingPathComponent:oldNameStr] toPath:[docsDirs                                                                                          stringByAppendingPathComponent:tempStr2] error:NULL];
    }

    return tempSoundPath;
}


-(void)deleteFile:(NSString *)str
{
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSArray *dirPaths;
    NSString *docsDirs;
    dirPaths = NSSearchPathForDirectoriesInDomains(
                                                   NSDocumentDirectory, NSUserDomainMask, YES);
    docsDirs = [dirPaths objectAtIndex:0];

    NSString *temp = [docsDirs stringByAppendingPathComponent:str];
    if ([fileManager fileExistsAtPath:temp])
    {
        [fileManager removeItemAtPath:temp error:nil];
    }


}