Thanks guys.
I just noticed the difference between the LM7805 and the 7805SR-C, the 7805SR-C has lower quiescent current (3mA vs. 5 mA), higher input voltage (40V vs. 32V), and better output accuracy (±1.5% vs. ±5%), and it has built-in filter capacitors so that no need for external components. but its much more expensive than the LM7805, doesn't worth the cost difference.
To change the output voltage I guess we should use those two equations
Io=Vxx/R1+IQ and then Vout=Vxx(1+R2/R1)+IQ*R2
am not sure how to calculate IQ!