You basically go to the sidebar, and scroll until you see the “Users” option. Click that to find the magic.
You’ll come to a page that looks like this page, this is the top part of the page, continue scrolling down it.
Scroll until you find the options to change and update your profile through Gravatar. Go onto Gravatar, in this step, you should already have a picture ready to be your profile picture.
Choose “Pick new image”, to start the process.
Upload an image.
Press that you accept, and prepare to have your profile picture changed, because after this it should be updated.