As far as will it fit or not I have no idea untill you try. however
costco will only install tires 3% larger in diameter which going from a
225/75 to a 245/75 is more than 3%. Not only are you going taller, but
also wider (from a 225 to a 245). Your best/safest way to go is to go
to costco and talk to a salesman, they dont work on commision, and will
give you the safest,best, and correct information. even if you dont buy
from them at least youll know what size you should get.