In case you don't know, it's nigh impossible to open a door if your car is even a little submerged.
With power windows, or even manual windows, you might find it impossible to roll-down the windows.
It doesn't matter if your right-side-up or up-side-down, until the car fills inside with water, the water level is the same on the inside of the door as the outside, the pressure differential will keep the doors closed.
You cannot smash the windows with your feet, with the possible exception of a high-heel shoe.
That's why it's a life-saving tip to keep a window smasher/seatbelt cutter in the glove box.

https://www.snopes.com/car-headrests-emergency-escape/
From Snoopes:
Claim: Car headrests were deliberately designed to be removed so that they can be used to smash windows during emergencies.
What's true: A removable car headrest can be used to break a window in an emergency.
What's false: Removable car headrests were deliberately designed to facilitate breaking windows in emergency situations.