I want to installa ceiling fan w heater and light in bathroom about it needs a 20 amp breaker. Breaker for bathroom is only 15 amps,

You don't. You run a new circuit.

The wiring in your walls is rated for the breaker that serves it. You cannot simply put in a bigger breaker.

Can you positively identify the size of the wires? If #12, you could use a 20 amp breaker.

Can you positively identify the size of the wires? if #12, you could use a 20 amp breaker.I didn't suggest this because he'd have to identify ALL the wiring on the circuit (highly improbable) and it would have to have been oversized from the original installation (highly unlikely). ;)

Stan, I was thinking that as well.
We can only use #12 minimum down here.