If you are running ArubaOS earlier than 6.3, "band steering" on the Virtual AP profile would move users to the 5ghz band. If it is 6.3 or later, "Client Match" will steer users to the 5ghz band. In general, you would also make the ARM min and maximum transmit power 6 db higher on the 5ghz ARM profile than the 2.4ghz ARM profile to "encourage" devices to go to the 5ghz band before the features above kick in.
Caveat: If the transmit power of your 2.4ghz band is higher than the 5ghz band, the clients might make their own decision to go back to the 2.4ghz band, and that could cause connectivity issues.