Locate the bicycle pump and place by your bike. Rotate the wheels so the valve is near the ground, to make the subsequent steps easier.
Check the current setting of the pump head. If it looks like below, it’s already configured for the Presta valve, and skip to step 10.
If it looks like this, it’s set for the Schrader valve, and you’ll need to flip the core around.
Unscrew the cap on the pump head.
Pull out the core. To help back out the core, flip up the lever.
Flip around the core so that the narrower side faces outwards.
Place the core inside the pump head.
Flip the lever down and push the core back.
Screw on the pump cap.
To help it fit onto the Presta valve more easily, slightly unscrew the pump cap, by perhaps a quarter-turn.
Locate the valve on the wheel.
Unscrew the valve cap.
Unscrew the valve nut to allow air to flow when the pump is connected. Air will only flow if the center is pushed into the tire.
Attach the pump head to the valve. But don’t start pumping yet! It’s not fully attached.
Further, still. You should not see anything but the bottom-most threading.
This is what it should look like when it’s fully attached. You should hear a brief hissing when it’s secure, but it should not continuously lose air.
You can verify that it’s secure when the pressure gauge reads a pressure without moving the pump piston. The current reading is just under 100 PSI.
Pull the lever back on the pump head to seal the connection.
That’s it! Pump your tire. If the pressure gauge starts from a low pressure and pumping it is initially difficult but the pressure gauge increases rapidly, stop and check the connection. You are probably not connected to the inner tube of the tire, and you’re putting the air pressure in only the pump, not the tire.
After you’re done, follow the steps in reverse to finish the process. Hold the valve stem to help remove the pump head. Remember to turn the nut from step 13 so that the center no longer moves (or wiggles). Also, don’t forget to restore the valve cap.