you simply loosen the pistol grip - carefully as to not loose the spring and detent that hold the safety - pull out the old , slip in the new and screw on the left side , reset the detent and spring and gently refit the pistol grip tighten the screw and your done - i just put one on my daughters AP4 , it took about five miniutes [i fumbled around with the detent and spring of coarse]

i was going to stick the other one i have on my carbine , but after handleing hers , i find it a PITA for my right handed hold