I would not recommend to change the woofer unless you are qualified to do a lot of homework. If you are after a bit more punch getting a woofer that is 1 or 2 db more sensitive could help, but not necessarily. The woofer in the cabinet has a specific impedance curve, it most likely has been compensated with a zobel circuit. IF the woofer that you replace it with has slightly different impedance, you would change the crossover point and add an overlap or cause a hole in crossover frequency.
