In the right corner (on the black menu bar) is a management panel.
Click on your username, and you will see the drop-down menu:
1 - This is your user control panel - here you manage, for example, subscriptions threads
2 - Here you change the settings of your profile (signature, avatar etc)
3 - Log out
Click on 2 - settings of your profile.
To change your profile, click here where you see the arrow.
On the left side shows all the options for editing the profile, as shown in this picture: