There are a couple of ways to do it safely. Safest is to remove bullet and powder, then put the rounds in the rifle and fire off the primers. It's not safe to attempt to reuse them, so firing them removes the problem of having to dispose of them as they can go in the general waste.
Alternatively, you can soak them for a few days in oil, before running them through the de-capper. You will need to thoroughly clean the cases before you attempt to reload them though, else the oil might well pool at the bottom of the cartridge and cause misfires when you reload them.
You can punch them out without firing them or neutralising them, but you need to do it gently and make sure you dispose of them safely.
Firing them is the easiest (and the most fun!)