Hey guys need help and don't know where to post. I bought a Imac 27" from a friend which is new. On the iMac is all his info. I can't sign into the App Store to update the iMac because his email is shown. How do I restore the iMac to factory which would delete all his info entered when he bought it 2 months ago. His info is hindering me with future use. I want to update this iMac but the app store is useless because I can't get his loggin info off iMac...Any help would be apprecaited