Getting new iMac 27' Retina. Giving old one to my daughter, and giving donating my daughters iMac to a school. What is the best way to wipe all my personal info? I have El Capitan installed on both. Thanks
Just follow the steps at this link. Use the instructions at the bottom for Mavericks (El Capitan works the same) and make sure you erase the drive first before you reinstall.
When you go to reinstall you will be asked for your AppleID. Go ahead and enter that to reinstall El Capitan. That AppleID is just used to access the download and is not saved anywhere on the computer.