You have to undo both sides! The drive shaft must be slid all the way over to one side in order to be removed completely in order to remove the track. There will be a bolt in the chaincase in the bottom gear into the shaft as well as a nut on the other side at the speedo drive head, it must be removed as well and if I'm not mistaken, the speedo drive head (three smaller bolts) will have to be removed as well.
Its not that bad of a job if you have something to lift the back of the sled and keep it there while you remove the track and suspension. Good time to disassemble, inspect and properly lubricate and repair any problems with the suspension too! I make up little grease zerk bosses and weld them on where Yamaha sometimes neglected to while I've got the suspension out. Of course I'm a little anal in that regard, I always say, if there just more lubrication in the world, there'd be a lot less friction! lol I like buying grease better than buying parts.
Good luck. G.