Reduce regulator PSI.
Vent excess pressure in keg.
Do that until its at the right carb level. Assuming about 40F, and a 'typical' CO2 volume, 10-12 psi is what you'd wanna carb and serve at.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10