Bicycle Mechanics - Shrader / Presta pump HELP!!!

I should know this by now but its been too long. I just got my old Pyramid Pro pump sent to me. I know it has a reversible shrader / presta valve on it and this should be simple but I cant figure out for the life of me how to flip it back and forth (i bmx and road bike). I dont know if I am missing a piece or what. Does anyone have an answer for this????

unscrew the collar on the pump head. Inside should be a rubber grommet and a little plastic piece that is hollow on one end (have this facing out for presta) and pointy on the other (have this facing out for schrader) Hope this helps. If not, here is link to a pictorial tutorial

http://www.bicyclinglife.com/HowTo/ConvertAPump.htm

Thank you... I dont think I have the appropriate parts anymore for the shrader which is why I am confused. they just arent there anymore...

usaully the parts are reversible. if it works for presta, just revesre the rubber grommet and plastic sleeve thing .

spend 20 bucks and get yourself a topeak smart head upgrade. no switching parts will do either bt just sticking it on the valve

The little plastic thing should flip over to reveal...da-da-da...the schraeder adapter. It's all in there.

i know it should all be in there and that easy.... but im pretty sure some parts have gone missing cause theres nothing in there!!!