http://www.cnblogs.com/jys509/p/5390505.html从这边看到的

-(void)viewDidAppear:(BOOL)animated{
    [super viewDidAppear:animated];
    [self hsUpdateApp];
}
-(void)hsUpdateApp
{
    //2先获取当前工程项目版本号
    NSDictionary *infoDic=[[NSBundle mainBundle] infoDictionary];
    NSString *currentVersion=infoDic[@"CFBundleShortVersionString"];
    
    //3从网络获取appStore版本号
    NSError *error;
    NSData *response = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"http://itunes.apple.com/cn/lookup?id=%@",APPID]]] returningResponse:nil error:nil];
    if (response == nil) {
        NSLog(@"你没有连接网络哦");
        return;
    }
    NSDictionary *appInfoDic = [NSJSONSerialization JSONObjectWithData:response options:NSJSONReadingMutableLeaves error:&error];
    if (error) {
        NSLog(@"hsUpdateAppError:%@",error);
        return;
    }
    NSArray *array = appInfoDic[@"results"];
    NSDictionary *dic = array[0];
    NSString *appStoreVersion = dic[@"version"];
    //打印版本号
    NSLog(@"当前版本号:%@\n商店版本号:%@",currentVersion,appStoreVersion);
    //4当前版本号小于商店版本号,就更新
    if([currentVersion compare:appStoreVersion options:NSNumericSearch] ==  NSOrderedAscending)
    {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"版本有更新" message:[NSString stringWithFormat:@"检测到新版本(%@),是否更新?",appStoreVersion] delegate:self cancelButtonTitle:@"取消"otherButtonTitles:@"更新",nil];
        [alert show];
    }else{
        NSLog(@"版本号好像比商店大噢!检测到不需要更新");
    }
    
}

- (void)alertView:(UIAlertView*)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
    //5实现跳转到应用商店进行更新
    if(buttonIndex==1)
    {
        //6此处加入应用在app store的地址，方便用户去更新，一种实现方式如下：
        NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"itms-apps://itunes.apple.com/app/id%@", APPID]];
        [[UIApplication sharedApplication] openURL:url];
    }
}

用于记录下以后可能用到
但是现在的appstore不会通过这样的功能
所以你只能与服务器的版本相互匹配.来实现提醒更新