Question about upgrading to Mountain Lion on two computers with two different users
I am running Lion on my MacBook Pro, and I intend to get the Mountain Lion upgrade. Someone else in my household has an aluminium iMac running Snow Leopard, so I was wondering how to upgrade that computer as well, considering that it has a different user with a separate Apple ID.
Can I open App Store and log in with my own ID temporarily to download the update? Or can I save the bandwidth and login-switching and burn an extracted installation disk image to a DVD and put that DVD into the iMac to upgrade from 10.6 to 10.8?
MacBook Pro, Mac OS X (10.7.3)