1) Login to your account
2) Click on your avatar/username in the top right and click 'Account'
3) Click 'Change' on your existing image
4) Click 'Choose File' , select your preferred picture which is already located on your computer
5) You can adjust the size of your photo by scrolling in or out on the image, or you can crop your photo to your liking
6) Once adjusted, click 'Set As Avatar'