Change code to work with 20x4 LCD instead of 16x2

Because I wanted more exaggerated looking peaks, don't get me wrong it looked pretty good on a 16x2 display but I just wanted a bigger display. Just trying to figure out how this code needs to be different to map to 16 pixels high (two rows) instead of 8 (one row).

I have extremely basic coding knowledge and are more used to tweaking values of existing code as opposed to writing stuff from scratch.