[ubuntu] New to linux, my sub is not working and I need some help with Terminal

I'm brand new to linux and upon ruing it for the first time I noticed my speakers are working fine but my sub is doing nothing. I've found the solution to my problem right here: (reply #2) http://ubuntuforums.org/showthread.php?t=1155761 but I lack the basic knowledge of Terminal to actually accomplish it.

I can use the linux version of File Explorer to find the find and edit the line of code, but it won't let me save it because it needs me to be the admin. Apparently I need to use Terminal to do this. I need specific, step by step instructions of what to enter into Terminal. Thanks for your responses and your time.

I am ruing ubuntu 16.04 LTS 64-bit.