I have an Early 2009 iMac now using El Capitan.
I read that I can install Sierra if I do this:
Things you'll need:
-A copy of the macOS Sierra Installer App. This can be obtained from the Mac App Store using a machine that supports Sierra, or if you don't have one, you can download a copy here
-A USB drive that's at least 8 GB in size
-A copy of the tool - Download here (Current version: 4.2.3)
*View changelog and download older versions here
I found this info here:
I compared the supported card in System Preferences under Network, Wi-Fi, Interfaces, en1 and I have "Airport Extreme (0x14E4, 0x8E)
which according to this info, is supported on my iMac.
I have an 8 GB USB drive.
It looks like I have what I need to do it.
Does anyone know if this is safe to do?
Thanks in advance for any help.