I think is better i change the rpm when i will ride for hours ?

Yes, by letting off the throttle and up shifting it removes the load on the motor and allows it to take in cool air and cool down the combustion chamber.

If it's always under constant load it will continue building heat eventually leading to oil break down and possible seizure.

Plus I think you have a paul turner pipe?  If yes, your silencer pipe is small and will also contribute to holding heat in the motor.