Talk:List of Mac OS versions/@comment-196.44.240.62-20150126111406/@comment-24886041-20150126232140

To upgrade to 10.5.8 (latest 10.5 version), you can go here: http://support.apple.com/kb/DL866

To upgrade to 10.6, you'll need to find a set of 10.6 install DVDs. Once you've installed 10.6, the update manager will update you to the latest version, allowing you to then upgrade for free to 10.10.

There are lots of caveats though:

1) If you're on a PPC Mac (G4 or G5), you're stuck on  10.5.  That's the latest OS X that will work on your hardware.  You might even find that 10.4.11 is a better choice.

2) 10.6 is the optimal OS X for older Macs.  To upgrade from 10.6 to 10.10, you'll need at a bare minimum 4GB  RAM.  It'll install with 2, but your Mac won't be very functional.  You can also upgrade 10.6 to 10.7 through 10.9, but there's not much of a reason to do so.