You can also increase the volume in the script.
In this table find at the top of the script:
Const SongVolume = 0.3 ' 1 is full volume. Value is from 0 to 1
And change that 0.3 to 1, like this
Const SongVolume = 1 ' 1 is full volume. Value is from 0 to 1
Many, or all, of my original tables have this variable. I always have this variable quite low so I can hear better the voices, as I find the music distracting 
Do this first
And if the volume if not high enough then you can increase the volume as xenonph wrote.
Hi, I had already tried this method also, it does not work ! Nothing changes, the volume doesn't go up, I can hardly hear anything
The you should need to check your Windows sound settings. Does other tables work fine? Mostly original tables, like for example my Mago de Oz? Which is a table based on the Spanish rock group Mago de Oz..
Hi!
I finally found and fixed the issue. It was a PupVideo pack for Ghostbusters that was overriding the table's audio, making it very low, even when the backglass audio was not audible. Essentially, it was compressing/limiting the table's audio to highlight its sound. With PinUp Popper, I set the FULLDMD volume to 60%, and magically everything is now balanced.
Thanks again for your support, you were very kind! Talk to you soon.