What file path are you trying to change it to? That looks like a mac file path, so you can add a windows one in filemaker like this:
clock.innerHTML=alarmLabel + \"<embed src='" &
Get(SystemPlatform) = -2 ; "file:///C:/Windows/Media/Alarm01.wav" ; //Windows
Get(SystemPlatform) = 1 ; "file:///System/Library/Sounds/Glass.aiff" ; //Mac
Get(SystemPlatform) = 3 ; "" ; //something for iOS
Get(SystemPlatform) = 4 ; "" ; //something for WebDirect
Better yet would be exporting your own alert sound file from a filemaker container field, and then passing that path in. That way you KNOW that the sound file will be where you placed it.