The website you want to make the avatar for should have some guidelines on size, dpi etc. Figure those out. Download the picture you want (be aware of the final size of your avatar). Open the pic in a photo editing software. Select change size, from those menus select the size the website requires. Save AS (use a name so you can find it easy) to your desktop, or somewhere you can find it easily. Go to the website you want the avi on and then select Upload. Voila. Without knowing what photo editing program you’re using that’s about as specific as I can get. Hope it helps!