After checking tire pressure, inflate them using compressed air until they reach the recommended pressure. If they're over-inflated, simply bleed them by depressing the center of the Schrader valve until they are properly inflated.
If you check tires after a few hours of riding, anything more than a 10% gain in pressure could indicate they're working too hard. If that's the case, you'll want to lighten the load and/or slow down.
