1. Go to mods\x64\audio\sfx\RESIDENT.rpf\
2. Right-click vehicles.awc and choose "export to Open Formats (.OFT)."
3. In your new vehicles folder you have to drag and drop the files and replace the old ones.
4. Now click on new and choose "import Open Formats file."
5. Choose your vehicles.oac. When it has been imported, you're done! 

If you do not want to replace all your Sirens, only replace selected ones: https://www.lcpdfr.com/forums/topic/90913-new-siren-hashes/

