How to Change Your Profile Image (Teams & Microsoft)

Go to https://portal.office.com
In the top right corner you will see your current profile image, click it.
Next, mouse over your profile image in the dropdown and click to open the upload new picture dialog.
Drag-and-drop or browse for the image you want to use as your new profile.
Make any adjustments and click apply.

Note: it may take a few hours to a few days for changes to be reflected system-wide.