The first method is to click your Avatar in the upper right corner and then click the preferences/ so you can scroll down to edit your Profile Picture. Don’t forget to Save Changes.
But method #1 above does not change 100% of your old pictures. If you look in your Profile the old Profile Picture is still there.
Which brings us to method #2. Go to your Profile, and click the large Profile picture. That will take you to a two step process to Upload and Crop your Profile picture. This second method will change only the picture in your profile. But your avatar remains as it was before.