- Go to https://tenhou.net/3/
- Click the gear icon on the top right
- Click right arrow button until you get to the SE settings page
- Paste in one of the following URLs: lite version or full version
The lite version only changes the sound effects that are voiced by default plus the SE at the start of the game and when a yakuman happens.
The full version changes all sound effects, use with caution.
Source for the audio files: https://booth.pm/ja/items/1428401