The ZenBook Flip 13 UX363 has some strong features, but upgradability is not one of them.
1. Remove the bottom plate
To get inside of this notebook you need to undo 9 Torx-head screws. Thankfully, ASUS has decided against playing the find the screw game. So, after you remove the screws, pry the bottom panel with a plastic tool, and lift it away.