Hi. I am a student of electricity and I have a question. I want to make changes to the control system of the basic code of the quadcopter (I mean the code for making the quadcopter with Ardino) but I don’t know which section should be changed. Can you help me?Please send an answer to my email. Thank yousajjadvarnaseri2012@gmai
If you mean Arduino, i suggest learning the programming language C / C++.
You cant just edit the Betaflight Software but you can get yourself a Drone that can be programmed by yourself.
What are you planning to change and what should your Drone do after you changed the Code?
Also how about reading the Replys of this post instead of waiting that somebody writes you an Email.
Luca 
Best place to start would to check out multiwii firmware. It is old and no onger active, but is fully written in arduino.
For us to answer you in a single post would require a book, so we cant do that there. But hope that multiwii can help get you started.