It's page 11-2 of the manual.
System Setup / User Preferences 11-3 DISPLAYThis tab is broken up into two areas, the Clock settings and Other Display settings control. Aside from the exceptions noted below, use the outer ring of the right-hand knob to select the row or field you want to change and use the inner ring to change the value. Use this tab to control
Temperature units (F, C)• Fuel units (gallons, liters)• Baro units (in Hg, hP, mB)