XML files that you edit are stored in your database. These files allways supercede those fom Odoo. That means that any update in Odoo will let them unchanged. Odoo will be updated but your edited files will still be used.

Odoo is automaticaly updated depending on how you install it : 

1. Linux users  typicaly use the package manager with the Odoo repository for nightly builds (see https://nightly.odoo.com/). There is no such thing on Windows.

2. Some users does their install by cloning the Odoo git repository and then regurlarly update it.

You can browse and remove your XML files if needed. First enable the debug mode, then go to the Settings app (not the settings menu), you will see a new Technical menu. In that menu, you will find your customized XML files under the User Interface and the Database Structure menu.

However, the best way to track, update or reverse your changes is to use modules : create a module (as a website theme) and put your XML files in it. It may sounds a bit heavy at first but it really save time, specialy because you can use Git to work on the module.