Nursery pots are a non-standard mishmash of insanity. There are 5-gal pots in tall, squat, azalea, and so on and so forth. An actual 5 gallon bucket is closer to #15 in nursery-speak. If they're root-bound, you could probably go up without disruption, but they're probably not there yet judging by the photos. You'd probably lose dirt from around the roots and they may be droopy for a few days. Really lovely plants!