NO!! You need to know what is coming out of the main circuit breaker box and hook the motor up to match. If not and you want to change you need to check and change anything not comparable with what you have now to the voltage you want to change to.
The size needed for the wire itself, 120 volt needs a larger wire to carry the current. If it's 120 now and you want to go 240 you are good. If you're 240 and you want to go 120 it might not be big enough.
The circuit breaker and the GFI or the circuit breaker GFI are best sized for the need and 120 volts will take more amps. The 240 volt system has more "pressure" to push compared to the 120 volt so it requires fewer amps.
You would need to ensure you have a correctly sized circuit breaker and or GFI. If you are going 120 to 240 you need a new breaker.
Most pumps will offer a 120 or 240 connection on the motor. The voltage the motor runs on is determined by how you hook the wires up to it. I think ... guess some of the newer VS (variable speed) pumps might only be 240 from what I've read. Don't have one and haven't worked on one so I'm not sure. The other thing is the horse power of the motor. Small ones are often only 120 and the higher ones only 240.
This is more trouble than it's worth

. . . what voltage are you running now and do you want to change ?? Much easier to answer that then try to explain all the differences.