Remove spring with needle nose pliers, grip aluminum part inside with same pliers VERY HARD and pull out... need good needle-nose that will not deform when doing so... once aluminum part is out (and small bolt from inside) you will see retaining ring inside... unscrew with needle-nose pliers... if it's giving resistance, feel free to dip it for 3-4 minutes in boiling water to soften thread-locker... voila... Assembly opposite way after replaced with another boot... screw retaining ring with plastic thug inside, place aluminum contact with bolt over it and hit carefully with thin longer part of metal (and hammer)...
As for E-series tailcap, your retaining ring is around the boot itself... it's probably threadlocked as well so a little heating is needed as well... just place needle-nose pliers in two small holes around the boot and carefully unscrew...
CPF has numerous threads on this...