Hey Cero!
You can place the RPA in the folder you placed the version you first installed the game with (Internal Storage/Documents/ahitr_storage/game) - Once there, you can delete the old version.
Alternatively, we have an installation guide here:
https://zanithone.itch.io/a-house-in-the-rift/devlog/583030/android-installation...
If you run into any issues, please let me know!