How to move up in weight without being outta shape

To move up, you obviously have to gain weight. To move up and still be in shape, that weight has to consist of muscle mass. To put on muscle mass, you need to hit the weights hard and eat enough to promote muscular hypertrophy (gain muscle). That usually means low reps and heavy weights and a caloric surplus (eat more calories - good calories - than you burn in a day). Check the boxing nutrition part of the site to walk you through developing a meal plan.

Before you decide to do this, just remember that you may be putting on mass but that doesn't mean you are going to be stronger. Ideally you want to fight at your natural weight and not force yourself to achieve a certain weight class. History is littered with boxers that figured they could move up a weight class and still dominate. Some of the biggest bodybuilders are not as powerful as smaller powerlifters - it is a whole different set of muscle fibers that dictate strength vs size. Done right though, you can put on weight and maintain your power as well.