Your tires should not be worn out already. Before putting new tires on, and then just ruining them in short order, fix what the problem is first. So yes, you are right to be taking it back and having alignment, etc checked.
If you are going to change to different size ( larger ) tire, check very carefully first to see if you have clearance above the tire. For instance, on my funfinder ( made by the same company as your trailer ) I have NO extra room above the tires for anything larger in diameter. If I were to install a larger tire, it would hit the fenderwell ( floor of trailer ) when the suspension goes to full bump. If you are not sure, then ask the tech folks at the factory. I did just that and they confirmed what I suspected.
Your trailer probably has 3500 pound Lippert axles under it, if I were a guessing man.
EDIT: also, if you were to want to go to a 215 tire, it is actually supposed to be mounted on a 6" wide rim. You most likely have 5.5" rims. Again, if I were betting, you have Sendel T03 rims. Man....they have sold a LOT of those in last several years !