Remove the twin wheel cutter plate and any thin shim spacers from the upper cutting head using a 6mm Allen key.Â
Pull the plastic strip away from the top end of the cutter bar and remove the pulley bracket by taking out the two small screws using a 5mm Allen key. Â
Slide the upper cutting head and the sliding toggle off the top end of the cutter bar. Slide the new sliding toggle in place ensuring it slides easily along the full length of the cutter bar. Replace the upper cutting head.Â
Refit the twin wheel cutter plate and the shim spacers, tighten the white plastic thumb screw to hold the cutting head in place.Â
Replace the two pulleys in the pulley bracket using a 4mm Allen (hex) key and a 10mm spanner/wrench and refit onto the top of the cutter bar. Replace the plastic strip.  Thread the cord through the pulley bracket and pass the cord down through the top of the machine. Â
Fix the cord to the ring fixed to the top plate of the machine and loop the cord under the pulley mounted on the Balance Weight.Â