1 simple clutch question???

sorry for dumb question like this!

my clutch is slipping at higher speeds (5000 rpm and above)i think it need friction plates or!!!
do i need to drain oil before i take clutch cover off to check checking the mechanical release and other componets?
this is my first time and dont want to have oil all over me and ground?
what should i check for???

I have the same problem on my 82 KZ-1000.
I have conclluded that I need to replace the friction disks because the clutch lever freeplay is adjusted properly (about 1/4 inch of freeplay) so, I know that it is not partly disengaged.
I have found that it slips if I hold it wide open but, if I back off, it grabs.
I suspect that the oil is contaminated by clutch friction disk material and you should change it anyway. If you lean the bike over on the side stand, you could get by with very little oil leaking out of the open clutch housing (if your bike has the clutch cover on the right side of the engine like it is on mine.
Spock

On a KZ650 if you attempt to remove the clutch cover without draining oil, you'll get about 3 quarts drain as you remove it. You'll need to drain first.

FWIW
I had the same problem on my B1 and I thought it was the plates too.
Once I got in there I found that my clutch springs were worn out and much shorter than my new replacement ones.
If your going to replace the plates then replace the springs too.
YMMV