1998 Oldsmobile Intrigue my trip odometer is set to kilomet

my odometer is been marking miles since i bought it. i want to change it to miles but by simply pressing the trip/odo it just changes from km to trip miles... thats it... i read the owners manual but it does not explain how to do it... is there a way to set it to miles? im trying to sell it but buyers dont like the idea of km's... thank you...