With the "New Experience" you cannot as far as I know.
While you cannot rename built-in styles, you can give them "aliases." With the "New Experience" the alias will follow the built-in name if there is room.
You can use the Styles Pane which will display both.
The switch for the "New Experience" appears when you click on the little megaphone icon in the Title bar and scroll down. A restart is required after you change it.
At some point, this "New Experience" will be there whether we want it or not. Be sure to use the Feedback mechanism in Word with a sad face to let developers know what you think of this. (I do not think any of them actually use Word.)
How do I give feedback on Microsoft Office?