How to safely replace your hitsounds

1. Open osu!

2. Go in the osu! options, then to skin. Choose the skin you want to use, then click on "Open current skin folder".

3. Delete all the audio files that start with "drum", "normal" and "soft". Delete the combobreak file too.
(some skins have the combobreak in the mp3 format, so you won't be able to replace it if you drag all hitsounds
in your folder, just delete it yourself)

4. Drag the hitsounds in the folder of the skin.

5. Re-start osu!
(you can alternatively switch to another skin and then switch back in the osu! options)

6. Enjoy the new hitsounds