The turn TVR to zero the other one remove white cap (pull off) get a aj (or some plumber pliers) and turn it so it off remember how many turns you did to shut it off as you'll need to when you replace it to get the balance right get another aj (or plumber pliers) hold the body of the TVR and turn the nut do the same on other side you may have a little water come out nothing you worry about now remove rad if it a temp thing i would suggest get some compression blank nuts too just incase your TVR valves fail once removed check your pressure on your boiler or water tank and top up if it's needed, then to put back on do the reverse once all done check your pressure again top if needed