half power.

i just found out i can go from 50 to 25 watts on my amp. in the back theres a switch that says high or low output (25 or 50W), so i put it on 25W, but now i don't know what to do about the ohms. it was originally on 8ohms, and the switch has either 8ohms or 4(16)ohms

which ohmage should i use with 25 W output?
heres the deal. If you had it set at 8 and it works, dont touch it.

If you had a 4ohm cab you would switch it. otherwise, just leave it alone.