IN case you were wondering -
You can edit your STEAMID which only affects your steam community name which is also what ends up in game as your name.

See the Edit SteamID button at top.

Just chage your name at the top of that page and save at bottom.

Your login to your STEAM account is not affected by this. SO to log into Steam would still be some email and password that you set up when you created a steam account.

Also note that NO special characters can be used. So no -= <> stuff.