Sometimes one of the couplers might need to be removed before that end of the shell comes off.....but many times not. This will be obvious if you look at it. Turn the engine up side down on top of a soft towel or clean rag. Look for plastic tabs on the side of shell......you can sometimes gently push toothpicks between the shell and metal frame to get the plastic tabs to release the shell from the frame. Sometimes one end will come out out first. Shells usually release and come off easily.
My experience is while of course you try to be careful to protect the details from harm like horns and railings, ect.,....they are so delicate....after awhile you are likely to have some minor damage. Just keep your eyes open and watch where small parts go if they happen to come off.
:: Mike Day :: N scale dismantler :: BNSF :: Canadian Pacific :: CSX :: NFS :: Union Pacific ::