You will need a security driver bit assortment set. (Harbor Freight for $7) Unplug electric. Remove screws from the back panel. Be careful not to use to much force. Use a screwdriver, not cordless drill driver. The upper housing is all plastic and flimsy. Take a picture of the back of the timer so you can reference which color wire goes where. Get the new timer and transfer wire from the old switch to the new switch one wire at a time. Remove the old switch by removing the security screw. Be careful not to let screw drop inside dryer housing. Turn switch body counter-clockwise carefully. Do not use force or plastic tabs could break. put in the new switch and secure with the security screw. Test run the appliance before putting the unit back together. This is also a good time to clean the dryer vent in the dryer and pipe.