This seems like something that might be easy, but I can't figure it out. I'm knitting a sweater for my dog. This is actually my third attempt.

The first two were either too big or I just didn't like them. On my third try, I actually did a guage, so hopefully the size will be correct. There are 2-3 spots in the pattern where it mentions trying it on the dog to be certain of fit. How in the world do I do that without losing my stitches? It's knit in the round.
Thanks for your help!
Colleen