Climb uder and PUSH the cable from the t-case forward to give it some slack up front, then pull the cluster further out...enough to get your hand(s) back there. I have not seen the screw on kind, just a hard plastic white clip. If you have strong fingers you can just squeeze it together and pull it off (installation is reverse). I've had to use some extra uumph with a pair of pliers, but if there is enough slack in the cable it should come right off.
When reinstalling make sure the little square "key" fits back into the square hole or the speedo will not fully engage and it will hop.