Hi Pete
There is 2 screws at the front of the drive but these are the same screws that hold the top on so you'll have already taken them out.
Then there is 2 screws at the back of the drive once you have taken the top off the RNS510, once you have got this far its a simple lift the drive up unplug the ribbon cable and swap over. Then put it all back together? Watch the front of the drive has it is fiddly to get back in place, if you do it wrong then is will not line up with the cd slot on the front.
Cheers
Darren