Can you tell if the breaker is tripping on overload or ground fault?
If it is overload and it has worked fine for years, it may be time to replace the breaker. Motors, especially loaded motors have a starting current which can be about 6 times the running load which can exceed the ampere rating of the breaker. Breakers are built to withstand this momentary inrush but can get weak over time and no longer be able to withstand it. It is probably a thermal magnetic breaker and the magnetic trip portion may have weaken after many cycles of heavy inrush. If the running current on the breaker has been close to it's rating of 50 amps, the thermal element may have weakened and be the cause.
Since your spa can be configured 3 different ways, it is possible that the breaker should have been a 60 amp from the beginning. Check to see if it is set up in the 60 amp configuration listed in the owner's manual, that is such that the heater, both pumps and the air blower can operate simultaneously.
If it is tripping on ground fault, you should have an electrician diagnose and fix the problem.