If you can see the gold plated pins on the rear of the phone, there is no cover on it, and it will not come apart any further.
If you are not seeing those pins, you only have to pull the back off the phone. The covers are only held on by magnets.
Look at the bottom of the phone. It should have a gap between whichever rear cover you have on and the phone itself. Put something plastic in there and twist. The rear cover should pop right off.