The Deltas use a different tire valve than most bicycles. It is called a "Presta" type, and functions differently than Schrader valves (like those found on cars).
Presta valves have tips that unscrew to allow air in or out. Unscrew yours several turns to get it all the way away from the valve stem:
You can let air out of the tire by depressing the valve core. It is a good idea to let a tiny bit of air out even if you plan to inflate -- this will prevent the valve from sticking.
If you don't have a pump that is designed to inflate a Presta valve, we include a small adapter so you can use a Schrader Pump to inflate your Presta equipped tire.
You can now check tire pressure with a guage or inflate with a Schrader type pump.
Once your maintenance is complete, remove the adaptor and screw the tip back in to prevent accidental air loss.