how can i upgrade from OS X 10.5 to OS X LION?
How can i upgrade from OS X10.5.1 to OS X LION?
iMac, Mac OS X (10.5.1)
First be sure your Mac meets the specs
2GB RAM is recommended as a minimum but IMO 4GB is more realistic.
Then you need to upgrade to 10.6.8 Snow Leopard (you'll need to call Apple to purchase a disc), then download ML from the AppStore and install.