Pop the legs off at the hips, take the legs apart at the thigh swivels, put the lower part of the leg below the thigh swivel into the new leg extensions and pop them back on the hulk. Some heat may be required, but not always needed. It is really simple. Hope that helped.
Exactly as my friend stated. I usually heat a small cup of water in the microwave and after I put them on the original leg,I dip the part that attaches to the hip in the hot water for a few seconds to heat it up. After it is a bit warm, it is easier to pop onto the t-bar.