I've done this many times on the Grado Green, Blue, Black, Silver, Red and Gold. You do not remove the guard. It is not designed to be removed. If you look at the photo you posted ( not the line drawing ) hold the cartridge body between finger and thumb. Take your other finger and thumb and take hold of the stylus assembly. Keep the cartridge in the position the photo shows and pull the stylus assembly down to the 5 o clock position. You might need to wiggle it a little side to side to ease it out. Fitting the new one is simply a reversal of taking the old one out.