question on updating to new app versions after update OS

**Edit: Found how to do it on Crackberry Accounts page**
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I'm a bit confused about app updating.
Since I've updated my OS to 5.0, many of the apps needing update, due to new version release, are offered to me in email as specific for the older OS which I had when I originally purchased the app.

How do you receive the version specific for OS 5, so you avoid receiving the version for an OS you no longer have?

Do I have to delete my current app and rebuy?
Does it happen automatically upon updating app?

Thanks in advance!