Its very simple!!
First of all you need to have a digital photo stored on your Computer.
Go to "Profile" next to the link from where you log out.
Check the "radio button" in your profile page
where it says "Upload a new photo"
then give the path of the place where your photo is stored or browse it.
Then click modify.
Note: Photo should be small(150 X 150).
Thats It !
P.S : Don't mind but even I haven't put up my photo. But I am sure it works!