I used UnityEX. I really don't know how to use Unity. What I did was export all of the contents out of the .assets file. All of the original content was still in the file. If you go to the (insert name)_Data foled, there will be a new folder labeled "Unity_Asset_Files". Open it. If you export everything, there will be two folders labeled "Textures" and "Sounds". Ann of the other files won't be in a folder. I deleted everything except the sounds folder. Ten I used Audacity to edit the audio. But I had to import the sounds by going to File -> Import -> Raw Data. Since the files were .fbs files, they won't be able to be imported normally. Then I re-record the audio, and then exported to the sounds folder again. Don't rename the file or it won't work. Now the edited / exported files will now be a .wav file, meaning it can be played back. Then delete all of the .fbs files. If you don't, the audio will be the same. Then go back to UnityEX, and double-click on the .assets file you used, and then click on "Import files". And if you did it correctly, the new sounds should be played in the game.
Hope this helped.