How do I modify the code

Hey guys. My company deployed a tutor based open edX. On an Ubuntu. I have access to the server through ssh. How do I start modifying open edX code? For example my first task is to disable signup button on the LMS and Studio. Am new to open edX, tutor, and Linux.
Pls I’d love an elaboration with terms I can figure out.
Thanks a lot.

@Nellymandela I can help you out. PM.