Steam is a game client that you can download on your computer. Note that Steam assigns you a SteamID, Steam Account Name and Steam Community ID. You cannot change the Steam Account Name, but you can change your Community name. The community name is the name that all users see on Steam-related forums and multiplayer gaming sessions.
Open your preferred Web browser. Navigate to "The Steam Community" Web page. Type your Steam username and password to log in.
Click "View Profile" on the right hand side of your account page.
Click "Edit my Profile."
Navigate to the "Profile Name" text box. Highlight your community name and press the "Delete" key.
Type the new community name.
Click the "Save" button at the bottom.