iT'S VERY SIMPLE....just follow the steps..-
1.GO TO UR ACCOUNT AND CLICK ON ''EDIT MY PROFILE''
another page will open...
2.THERE WILL BE AN OPTION LIKE-''CHOOSE FILE'' UNDER A HEADING -CHANGE PROFILE IMAGE (at the top)
3.CHOOSE THE IMAGE THAT U WANNA UPLOAD FROM UR FILES....
4.CLICK ON UPLOAD...
another page will appear as-''YOUR AVATAR PREVIEW''
you will see the image that u selected...and a small box...at the top with dotted boundary....
5.JUST SELECT THE PORTION OF YOUR IMAGE THAT U WANT TO SEE AS UR PROFILE PICTURE BY STRETCHING OUT THE BOX AT THE ENDS....
6. LASTLY, CLICK ON ''SAVE MY AVATAR''....
that's all u have 2 do.....