Ask a friend to stand on the outside of the door while you are removing the hydraulic door closer. This helps prevent people from opening the door while you are working. If you do not have a helper, close the door and engage the door lock to prevent people from opening the door from the other side.
Set up a step ladder under the door closer. Pull the cover off the closer if necessary to access the four mounting screws. There is a mounting screw at each corner.
Remove the screw and washer securing the lower half of the door arm to the top of the closer with a Phillips-head screwdriver. Pull the lower arm off the top of the closer. Remove the pin securing the upper door arm to the bracket on the door frame. Remove the arm completely from the bracket.
Take out the self-tapping screws securing the door arm bracket to the door frame with a socket wrench or Phillips-head screwdriver, depending upon the fastener head. Repeat for the four mounting screws securing the door closer body to the door.