Acura 2008 RL Owner's Manual page 246

Remote Audio Controls
On U.S. models except Hawaiian
If you are listening to XM Satellite
Radio, use the CH button to change
channels. Each time you press the
top ( ) of the button, the system
goes to the next preset channel.
Press the bottom ( ) to go back to
the previous preset channel.
To select a different channel of the
category you are listening to, press
and hold the top ( ) or bottom ( )
of the CH button until you hear a
beep.
240