SHELBY GT 350 Member
Joined: Sep 2010
Location: see user name
You talking about the Schraeder valve - little spring loaded thingy that looks the same as a tire valve?
There's a special tool for them (Schraeder valve removal tool) and they just unscrew.
Once you put new ones in, hopefully you are aware that you can't just hook up a can of 134a and fill the system. Prior to filling, a vacuum pump must be hooked up to it, which serves two purposes - verify that the system is sealed, because it won't be able to pull and hold vacuum if there are any leaks; and the other is to remove atmospheric moisture from the system which will have gotten in when you were changing the valves - refrigerant and moisture do not like each other, in any amount, and making the two hang out together will cause corrosion of parts and components internal to the cooling system.
Regarding the vacuum pump and properly recharging the system this is best left to a shop, just in case there's any ambiguity there.
2001 GT Convertible
All the usual bolt-on's /200 I6, C4
And a few Explorers too... 2008 4.0 XLT 4x2, 1996 XLT 5.0 4x2, 2003 Sport Trac XLT 4.0 4x4