Hey, Welcome to the forum
I hope you enjoy your stay
To change your Display Picture go to the "Profile" tab at the of the page just below the banner.
Once you click on Profile a row of links should show up under the tabs
(Information | Preferences | Signature | Avatar | Friends and foes | Notifications | Topic(s) being watched | Favourites | Character sheet)
You want to click on Avatar to change your Display Picture.
There you can upload an Image from your computer or use a URL
Displays a small graphic image below your details in posts. Only one image can be displayed at a time, its width cannot exceed 150 pixels, the height cannot exceed 300 pixels, and the file size cannot be higher than 64 KB.
Hope that helps