Download and install Audacity; a free, open source, multi-platform audio editor.
Import the wav file of the show.
highlight entire file
from one of the menus, select amplify (how much depends on where the signal peaks), when happy with results, save/export or whatever audacity's option is
I'm not at a comp that has Audacity on it so can't be more specific. Audacity does have a rudimantary help file which will explain the basics, but not much else. If all you want to do is boost the signal, it is all you'll need and it can do many other things as your editing needs expand.
http://audacity.sourceforge.net/ I recommend the last stable release (1.2.6)
< also search ts for "workflow" by Brian Skalinder who has posted numerous detailed workflows for various editing programs >