Iirc you need simply to remove the nut, and the old lever should slip out of the assembly. Be aware of the spring which pushes back the indent from position 1 to position 5. I think I had mine so there was minimum tension on the spring, then just dropped the old lever out, slipped the new one in, made sure the indent (1 to 5) still functioned properly, aligned the hole with the mounting bracket, slipped the bolt back in, threaded the nut, and tightened.
BUT, do LUBE the pivot point where the cable enters the lever assembly. I used hi temp grease, just a dab or 2.