Basically you just remove the cylinder, remove the cam cover, and unscrew them they are a standard RH thread, but they can be very tight and usually they will come out easier with heat, make sure that your spanner is a good fit otherwise they may round off, replacement is simply the reverse of the above
Butch needs new tappet heads, his exhaust tappet head is broken. Wouldn't it be possible to just compress the valve spring and remove the tappet heads without removing anything else?
Drop me an e-mail, i'm in Perth, not replaced the tappet head before, but if Ian say's there's enough clearance to get it out by compresssing the valve, it's not hard, even to slip the head off is no big deal, but i doubt its needed.