Well from one not so total dunce to another -
Start by making sure you are on the new ab beta website www.beta.the answer.co.uk
Go into 'my profile' you down to where the avatar section is click browse button it will then open a box which shows you all the files on your pc select the file by double clicking on the file you want. It will then revert back to your profile again where the name of your picture file will show in the window next to the browse button, click the submit button.
The file size has to be smaller that 100kb and it say's it has to be a 'giff' file I do not know what type of file that is but I used a 'jpeg' file.
It might be easier to move your file you want to your desktop for example or a new file beforehand so it is easlier to find when you click the browse button.
Hope this helps