Go to "Settings" upper right side....
Go to "edit profile picture" under "my settings" left side top
Then either paste in the URL, or upload it from your computer, if you upload keep in mind the max size for profile picture is 250 by 250 pixels or 103.1 KB...... You may need to use a photo editor to make picture smaller if yours is too big. If you click on picture and go to properties, it will tell you the size of the picture.........
"Photobucket" is a good site for storing pictures and has a good editor if you don't have one and it is free.................