Hi David, 40 MHz is a band of frequencies, and there are quite a few that are legal for a boat. They are controlled by a little component called a crystal, one in the model and one in the transmitter. They usually plug in, but sometimes are soldered in. The use of different crystals on different frequencies allows several different models to be on the water at the same time.
Changing the entire radio control to a type that works on a different band such as 2.4 GHz can be challenging for a novice, and not always practical on many bait boats. We would need more information on yours to give a better answer on that aspect. If you are lucky and the model has a separate receiver, then it's relatively simple, just an exchange of equipment.
Why do you need to change frequencies?, is something not working properly?
Chas