I am in the process of a ground up restoration of an 8B. While you could, in theory, leave the lift cylinders in place with one end connected and the other end loose, I would not recommend it. I took my cylinders to a local hydraulic shop. They fought with both of them on the bench and finally got the ends off to do seal replacement. No way did I have the tools, torches or enough hands to loosen things up. Best $350 I've spent recently.
But if you want to try in place...
Start with detaching the bucket from the boom. The boom will need to be raised in order to access the lift cylinders to get room to work if you try to do the seal with repair with the cylinders in place. Scope out how high you have to lift the boom to get enough room to work before you remove cylinder bolts. BLOCK THE BOOM IN PLACE. IF IT DROPS, WHILE YOU ARE WORKING UNDER IT, YOU COULD BE SERIOUSLY INJURED OR KILLED. SAFETY IS PARAMOUNT!
Assuming your 8B has the ROP (roll over protection) cage in place, you'll need to tilt that up or remove it depending on which version you have. You need to do this to access the bolts holding the lift cylinders to the boom and frame.
There several versions of cylinders on the 8B, see the attached PDF with this post. Best of luck to you.