If the other cyl was made /fitted o your gun, i should have the last 3 #s of the ser # engraved on the face of the cyl. If it matches, your all set. Ifnot, Ruger can match it.
To change. Push little pin in front of cyl in frame. While holding pin in, pull out on long cyl pin (that goes through the cyl.) lastly, open the loading gate and pull the cyl out that side. assembly is just the oposite.