I just bought a house with a jaquzzi that was installed by the previous owner. It appears that they wired it to an existing circuit run that is only pulling 15amps. So if the lights are on in the bath room and in the closet, when we turn on the jaquzzi it trips the breaker. Before I open up the ceiling and make a mess running a dedicated 20amp circuit to the jaquzzi, can I just change the circuit breaker to 20 amp and leave everything else alone?

If it is #12 yes, #14 needs to be protected by 15 Amp Breaker.

You will be happier with a dedicated circuit.

Your tub should be on its own dedicated circuit & if it has a heater that also should have its own circuit. That's all there is, the home owner did not follow code

Also should be gfci circuits