downgrading OS
my macbook is too old for 10.12 and I need to downgrade. If possible, which version should I use (late 2009 model) and how do I do it?
MacBook, 10.12
User profile for user:
CarlAVII
User level:
Community Specialist
Hi 99,
Thanks for coming to Apple Support Communities for help today. It sounds like you want to revert to an earlier macOS on your late 2009 MacBook.
Your MacBook is compatible with macOS 10.12: How to upgrade to macOS Sierra. If you post any specific issues you may be having to Apple Support Communities, you may find the help you need.
That said, if you want to revert back to an earlier macOS, the easiest way to do this would be from a Time Machine backup: Restore your Mac from a backup.
If you don't have a Time Machine backup, you would need to go into Recovery and reinstall macOS: How to reinstall macOS from macOS Recovery. You would still need a backup of your data, Reinstalling an older macOS would erase your drive. See the section under "Start up from macOS Recovery". The key combination you would want is shift-option-command-R. This will "install the macOS that came with your Mac, or the closest version still available." You would need macOS 10.12.4 installed for this key combination.
I hope that helps.
Have a fantastic day!