Since they're DC fans, the only way to change them would be to vary the voltage. FWIW, my MB does have a variable speed utility that does indeed vary the speeds of the fans, based on the temperature sensed in the case. It appears they just vary the DC voltage to do that.
I'd say your MB should mention this capability, or it probably isn't possible. I doubt it's possible to increase the speed over the design maximum without damage, and I'm not sure why you'd want to try.
I'd say your MB should mention this capability, or it probably isn't possible. I doubt it's possible to increase the speed over the design maximum without damage, and I'm not sure why you'd want to try.