Re-Tubing a Peavey Power amp

Ive got a Peavey classic 50/50 power amp that uses 8 EL84's 2 12at7's and 2 12ax7's , My question is can I change these tubes myself? Do they need to be biased somehow? the manual says nothing about changing tubes.. I would really like to do this myself because its already 160$ for just the tubes and i dont wanna pay the local amp tech who charges $40 an hour.. any help would be much appreciated.
-mp-

I am not an absolute in tube savoy but I believe if each set of 4 84s are a matched set you should have no problem. Meaning you have 2 channels that use 4 power tubes per side. The pre's seem to be no big deal to me either. Hope some others can give better input.