To post a picture:
1- Go to the bottom of the page to the Quick Reply Box and press 'Go Advanced'
2- Once on the new page scroll down to the Additional Options - Attach Files
3- Press 'manage attachments'n and a window will open. In the window select 'Choose File' and find your picture. When your finished press upload.
For your avatar this is how I got it:
1- In the top right hand corner there should be 3 GSD heads. To the right of that your username should be there with some other info. Select 'Upgrade my Membership'.
2-On The new page there should be some colourful columns in the middle and your control panel on the left hand side.
3-Under 'Settings and Options' click 'Edit Avatar'. On the new page click Choose file and follow step 3 above.
Hope I helped!!