Firmware Modification Basics? Changing app_adc.c

Hello,

I'm new to the VESC and having fun messing with it, but it seems many of the things I want it to do with ADC inputs I'm having to create external analog circuitry.

I'm sure that changing the firmware / code could create the same effects for me, but I'm completely lost as to how to make these updates.

Specifically: I want to have it look at ADC inputs and do certain if / then / else with it. I'll figure out the coding later.

Where I'm stuck: I'm looking at the app_adc.c file. Modifying that and saving it is self explanatory...I assume.

What are all the steps to:

Taking that modified file and putting it into the firmware to upload to the VESC?

Everything I find on the process is very high level.

Thanks!