To cut the ribs take a good sharp meat knife in one hand and the rack of ribs in the other. It is easiest to carve ribs by setting them standing up on the meaty side. (bones should be sticking out a little on the top side). Now you can simply side the knife down through the rack between the bones. If you guide it down directly between the bones you should be able to pass the knife through easily.
If your ribs are "fall off the bone" tender then you want to lay the ribs down, bone side up, and cut them the best you can. If the ribs are very tender the meat will tear apart more easily than it will cut. Be careful or you will lose the shape of the ribs and simply end up with a pile of rib meat.
The last part is to take note of your ribs. Too tender? Not tender enough? Too sweet? Too spicy? If you record your process, the next time you smoke a rack of ribs you will be able to make the necessarily adjustments to the process.