Profile pictures can be a bit awkward. First, you need to have it saved online somewhere. Then click on the image and select "Copy image address". This picture has an address, so right click on it and select "Copy image address":

Click on where your profile picture would be, in the top right of the page. This will give you a drop-down menu. Click on "Settings" in that menu.

You post that image address into the text fields there and save it. That will change your profile picture to this one. To paste, use Ctrl+V together.

Hope this helps,

DM-Jo