I m using ipad mini i got update message from app store regarding garageband 2.1.1 and i hv download full software of garageband through itunes but software could not be installed bcz itunes sync error

Try resetting the App Store:

Close the App Store completely from the app switcher window by double clicking the Home button and swiping up the App Store preview pane until it disappears from the screen. Then sign out of the iTunes Store (in Settings).

Then do a forced restart. Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears.

Then sign back into the iTunes Store.

Also try going to Settings > General > Restrictions > and make sure that the iTunes Store, Installing Apps, Deleting Apps, and In-App Purchases are all under the Allow section. Test installing again.

It seems you have downloaded this update on your computer and are attempting to sync it through iTunes. I would try updating this app directly through the App Store found on your iPad. Are you having trouble syncing any other content through iTunes sync like music or photos, etc?