First, navigate to your profile page by clicking on your photo or name in the top-right corner.
You'll see a white box with some basic info at the top of the page, (what we call your "Intro Box"), including your profile photo and username. In the right corner of that box, you'll see a white button labelled "Edit."
When you click that, the edit pop-up window will open. The third field on the page will display your current email. Click the "Edit" icon on the right side of that field to change your email.