This is a common issue thanks to the use of automatic form filling (auto-fill) that is available in most web browsers. You may think it is helping you pick the city and state in your address and not see that higher on the page it is also changing your name to whatever name is saved in the browser for that address!
Good thing it is an easy fix from the Account menu on your Dashboard.
- Open the Account menu and click the pencil (edit) icon in the About You section
- Make any edits or updates you like and hit Update