Cock your crossbow. Pull back on the draw string, or use the crank to place the bow in full-drawn, firing position. Lock it in. Make sure that you don't have a bolt in the bow's groove. Put the safety on. Even without a bolt in, you don't want the crossbow to discharge while you are changing the string. An accidental discharge could result in injury, a broken string or damage to your bow. Thread the new string along the same path as the old one. Insert your new string through the bowstring loops and situated it over the nockends as well. Ensure proper placement of the new string. Double-check both the string's threading and make sure that the string is firmly seated in the nockends. This step is very important because if you haven't threaded the new string properly, the bow could accidentally release during the next step. Get a firm grip on your string and pull it up and away from the bow. Make sure you have the new string securely fastened in your hand, as some bow weights discharge with 60 pounds of force or more. Remove the safety and release the trigger. Gently and firmly allow the bow to contract. Lower the string back toward the uncorked position with even force until the bow has fully relaxed. Remove the old string. You can unthread it by starting at either nockend.