HCA: Hermit Crab Association

hey yall!
so my biggest crab swapped shells the other day, FINALLY! but he moved into a shell that's smaller than the one he had. should i try to get him to move into a bigger one or just let him be? i have a small crab and him, so that's why i had different sized shells in the tank

Make sure he has other sizes available at all times, but you can't force him to choose somethibg different. Try to have the same shell in a few larger sizes just in case he likes the shape.