Before you start, make sure it does not have a fibreglass lead. You remove the lead screw drive. There is a nut that is removed by a set of flat nose pliers as it is a slotted nut, hold the focus knob when turning the nut. The metal leadscew bearing or support is held in place with three small self tappers. If there is a spacer on the front of the lead screw, held in place with a circlip, make sure it goes back in the same place, as it stops the lampholder getting too close to the front lens. Once you have removed the lead screw you can pivot the lampholder sideways to get at the screws underneath. It is a while since I have replaced a lampholder, I may take out the other non lead screw side as well. I place all of the parts in a line as I remove them to make sure it is reassembled in the correct order, as there are also washers.