it's always good to have a larger tank to reduce the aggression, but the question is whether it's a good idea for an upgrade for the sake of one fish financially. if you're well-off, then by all means be my guest. if otherwise, i would just return or rehome the fish and make sure you get something not as aggressive. there's really nothing you can do to a limited size tank with a fish that's known to be an aggressor even though it's labeled as "semi-aggressive". you can easily swap it out for a flasher wrasse or firefish or royal gramma while maintaining the lively color in the tank.