Plug the drill's power cord into the electrical outlet or insert a charged battery if the unit is a cordless model.
Set the drill's direction indicator to reverse. Hold the spindle with one hand and depress the trigger with the other to loosen the jaws of the spindle. Remove any bit from the spindle.
Insert an Allen wrench in between the opened jaws and into the screw in the back of the spindle. Loosen the screw by rotating it clockwise to remove the screw. Set the screw and Allen wrench aside.
Hold the spindle securely with your hand once again and depress the trigger with the other hand to loosen the spindle from the drill's drive shaft. If the spindle slips in your hand, hold it with a large pair of vise-grip pliers to loosen it from the drive shaft.
Rotate the spindle counterclockwise on the threaded drive shaft until the spindle is removed.