i have the demo version how i can change my team during the game
I believe you can't
I think you can actually, in one of the Menus you can change team, but i have the Full game not the Demo.
Try opening the console (I use the deluxe console or whatever you call it with ctrl + ~ and then type "server changeteam". I haven't tried it yet but I've been looking myself for this function. I've read it only works if the server allows this. Also if you press F1 when playing and scroll through the pages I've also heard the console commands are listed.
Oh and I also have the full game not demo, hope it still works for you.
if u set it to a sertent team in player set up u can ingame but if u did not set auto when u die u should beable to slect the team unless it is co-op then there is jsut one team!