Things You'll Need
Instructions
Open your "Friends" list by right-clicking the Steam icon in the system tray, located on the bottom right of your screen.
Right-click on your current name, and select "Change Profile Name..." from the drop-down menu.
Replace your current name with whatever you like in the "Profile name" field to the right of your avatar. There are no restrictions on what your name may be, and it doesn't have to be unique. Click on "OK" to finalize changes.