I have LR 2 Full Editon and upgrades 3 and 4. Can I delete Upgrade 3 to save hard drive space?
Every install is the full program, so they are not dependent on an earlier version being installed. The license keys are all that is important in the event you need to install on a new or second computer.
So you can go ahead and uninstall/remove the earlier versions, one everything is working fine with the tatest version