Hey Kmas508, it's pretty easy, all you do is up the top of the page, under the header, click on "User CP" once you do a page will come up with details like your user name and password and email and age etc. you don't need to worry about that, what you need to do look up the top of the page, right under where you clicked "User CP", and click on "Avatar". Once your on there just follow the instructions to upload the picture.
Hope it helps. Any further problems don't hesitate to ask.