tubes in a Copland 504???

I know there are 4 6550,s ( btw can I use KT-88,s) But not sure on the rest. Looks like 4 12au7,s and 1 12ax7 as a pre tube. Please help me out. I just got the amp and am looking to upgrade the tubes.
CAN you use KT-88,s??? Please thats the main concern now.
Yes you can use KT-88s, but you may need to adjust the bias to get the most out of them and not burn them out too quickly.
OK How do you adjust the bias? I am assuming its the little blue and white pots in front of each tube but as I said assume. Help if you can.Thanks