Move the twin wheel cutter to the top of the machine (adjacent to the open channel) and lock it in position using the white nylon locking screw. Ensure that this is done tightly.
Hold the twin wheel cutter on to the cutting head whilst removing the screw with a 6mm Allen Key.
Slide the twin wheel cutter out through the open channel in the main body and lift it out.
Reverse the procedure to fit the replacement twin wheel cutter, ensuring it is properly located flat against the cutting head before fastening the screw with the 6mm Allen Key.