Jim, OK, if you're just talking about the damping oil, it's pretty bloody easy!
Remove the gubbins on the top of the right leg (Poploc cable and the twiddly little gold knob if you have one) then undo the circlip and lift off the blue lever/dial. Use a 24mm (I think….) socket to undo the 'bolt' in the top of the leg and withdraw the motion control damper in one piece. Drain the oil (Compress the forks a few times to get it ALL out, and keep draining) Refill with new 5wt oil (120cc I think in Pikes, but it's on the RS site if you look hard enough, under 'Specs' IIRC) and refit all the bits.
When you refit the damper, just nip the 24mm 'bolt' up gently, don't swing on it!
And, FFS, DO NOT USE AN ADJUSTABLE SPANNER instead of a 24mm socket or ring spanner. You run the risk of knackering the flats on the 'bolt'
🙂