How can I delete a plist programmatically?

NSFileManager will allow you to delete your file using removeItemAtPath:error:

+ (void)deletePList {  
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *path = [documentsDirectory stringByAppendingPathComponent:@"mobile-watchlist.plist"];

    NSError *error;
    if(![[NSFileManager defaultManager] removeItemAtPath:path error:&error])
    {
        //TODO: Handle/Log error
    }
}

Here's how.

    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:@"mobile-watchlist.plist"];
    [fileManager removeItemAtPath: fullPath error:NULL];