Check Update Available App Store

You can easily ask the App Store to return your application info:

e.g. https://itunes.apple.com/lookup?id=441252681

In the json response, the "info" field is what you're looking for, and you get it updated for free!

See the official documentation here.

I currently use a library available on Binpress that does the checking for you. As of this post the library is free.

http://www.binpress.com/c/615/6592

You could also use your own notification message when you push an update rather than using an automated check (available on Binpress and again also free as of this post)

http://www.binpress.com/c/662/6592

NOTE: I am in no way related to or receiving payment/compensation from the Binpress OP

Just use ATAppUpdater, it is 1 line, thread-safe and fast. It also have delegate methods if you would like to track user action. Here is an example:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    [[ATAppUpdater sharedUpdater] showUpdateWithConfirmation]; // 1 line of code
    /////////////////////// OR ///////////////////////
    [[ATAppUpdater sharedUpdater] showUpdateWithForce]; // 1 line of code

   return YES;
}

Delegate methods:

- (void)appUpdaterDidShowUpdateDialog;
- (void)appUpdaterUserDidLaunchAppStore;
- (void)appUpdaterUserDidCancel;