The Store app only checks for updates every 12 hours I believe, and there's no known way to force it to fetch app updates.
All you can do is pin it to your Start Screen and wait for it to update. Alternatively, you can get an update immediately if you just search for the app your trying to update. While it may not notify you, you can still update any app so long as you can search for it in the store or obtain and store link.
Best of luck, friend.