Unplug the dryer from the wall.
Remove the screws from the face of the control panel.
Remove the screws from the back of the top panel if you are servicing a front-loading Hotpoint dryer, and slide the top panel forward to release it. This exposes the top of the control panel. Remove the screws from the top of the control panel to release it. Slide a putty knife under each side of the control panel if you are servicing a top-loading dryer and push back on the control panel to release it.
Locate the dryer timer knob. Pull it off the front of the control panel.
Remove the screws mounting the timer control to the control panel. Pull it off.
Pull on the wire connectors on the timer using a pair of pliers. Pull at the connectors, not at the wires, to prevent damage. Mark which wire goes to which terminal.
Connect the wires to the new timer and reassemble the dryer.