Click "edit profile." From there you can remove an existing picture and/or upload a new one. Click "browse" to find and upload your profile picture.
Note: Give your file a meaningful name. Don't upload "image.jpg" as it may overwrite another profile picture of the same name. We recommend you name your file Lastname-Firstname.filetype.
Note: Your image will be resized to fit the various style conventions set on the site.