i need to remove the valve stems but i'm not sure on how to do it

 

you cut them at the base with a straight razor, you shouldnt reuse them.

Unless you mean the core which you need a special tool or thin needlenose.

 

Right. Some valve stems have the tool on the cover to remove the "guts" of the stem, this will allow the air to all go out. it's sort of like the tires on a remote control truck, sqeeze the tire, the air goes out, then it suck air back in.