If you're a Mac user, press Command+Return while any item in a list view is selected to toggle editing of an item's name.
I find this to be much easier and faster than using the Info window or the delightful "Click to select. Wait a moment and then click again to toggle editing, but don't click too soon or else it'll be a double-click and you'll start to play the item."
If you're a Windows user I assume you press F2 to rename an item, but I've never used iTunes on Windows.
