windowsphone.com if you've had a previous update it'll be in your purchase history.
For those that have been unable to receive the recent Nokia updates and wish to manually do so.
Basically go to the above site on your phone, log in to your Microsoft account and go to "Purchase History". From there you can see all the apps you've purchased/installed. For the applications that say "App not available on the Web...", you can just click on the name of the app, it will open up the marketplace where you will find it and manually update. In my case, I found "network+" and "extras+info" from Nokia have not been updated (because they were undiscoverable on the marketplace and my tile was not updating for them ever).
NOTE: after updating "extras+info" and "network+" RESTART your phone, you will notice that in the settings menu the application's name becomes a physical path (e.g. C:\APP\blah blah) prior to restarting.