Which version of GarageBand do you have installed? Are you using the older GarageBand '11 or the new GarageBAnd 10.0? You cannot update from GarageBand '11 to new GarageBand 10.0. It is a major new release and requires a purchase-
Apr 17, 2017 Without this, I find it to be a huge step backwards. In the purchase section of the Mac App Store is the old version. I have both versions on my Mac just in case I ever need to use the. GarageBand is a fully equipped music creation studio right inside your Mac — with a complete sound library that includes instruments, presets for guitar and voice, and an incredible selection of session drummers and percussionists.
The error message ' not purchased by this Apple ID' will be displayed, if GarageBand is not associated with your AppleID. You do this by 'Accepting' the app at the AppStore:
Open the Mac App Store's Purchases tab. Do you see GarageBand there with an 'Accept' button? I
Now try again the 'Updates' tab.
3.If the update for GarageBand 10 is not showing as free, contact the Support: http://www.apple.com/support/mac/app-store/contact/
The regular update may not work with a purchase through your school. Apple Support should be able to sort this out.
Nov 16, 2014 2:48 AM