Replace valve seals without taking off head

It has been posted before but can someone give me the run down on exactly what needs to be removed to replace the valve seals. Looks like some head bolts need to come out and the cams removed. Rocker arms removed? Best tool for the job?
I also read a previous post that the oil problem was a stuck scraper ring. The front exhaust ports and the 4 inlet ports are good but the rear exhaust ports shows signs of oil. Adding to this that the bike had filthy oil and was only run for 10 km in the last year is this likely to be normal leak past the seals on two cylinders? I have wiped the valve stems in the exhaust ports clean and wait to see if any oil returns to them over the next few days. If so = stem seals.

I bought a tool from a guy in the US to do this job,fantastic bit of kit that required cam and rocker removal.
I then realised only four bolts were holding the head on.
For the cost of a gasket I opted to remove the head and do a proper decoke.
Could have bought 10 gaskets for the cost of the tool,every day is a school day

Thanks for that Bif. I wondered whether there might be a gasket leak etc after removing so many bolts. If you could just remove the cams like on an inline four without removing some head bolts it would probably be ok to do this.