garage band update

Which GarageBand version do you have? And which update do you want to update to?

the last few days there have been some older software versions missing from the App Store, probably because Appel is preparing for the release of El Capitan on September 30.

http://www.macrumors.com/2015/09/29/older-software-returns-mac-app-store/

Try, if the updater from the support page will work for you. The download link is here:

GarageBand 6.0.5

I'm dealing with the same issue. When the updater linked to above is run, it displays this message: "GarageBand6.0.5Update.pkg can't be installed because its digital signature is invalid."

The certificates for installers are only valid for a limited amount of time. The updater has been posted in March 2012.

Set the date of your Mac to a date in April 2012 in the system preferences > Date&TIme panel, then restart the Mac and try again to run the updater.

No luck. The same error message is displayed.

Does GarageBand show on the fourth tab of the App Store, in your Purchases history?

Then try the following:

• Move the incompatible GarageBand version from the Applications folder to the Trash, but don't empty the Trash.
• Restart the AppStore and sign into the AppStore with your AppleID from the Store menu.
• Open the fourth tab "Purchases" and try to reinstall GarageBand from the Purchases tab.
• If that does not work, put GarageBand back from the Trash and contact the AppStore Support - there is a Contact US link on the main page of the App Store, in the "Quick Links" section.

GarageBand does not show in my Purchases history.

Then you need the Help of the App Store support. Give Apple a call.