If you prefer Command Line Interface , VI or VIM Editor is your best choice [ try command vi <filename> or vim <filename> from Command Line ]. But if you are not familair with it, I suggest you to go through the documentation first and be familiar with it, else you may corrupt the file easily. You may refer
https://www.cs.colostate.edu/helpdocs/vi.html ato start with and it appears to be a nice document to me.
But there is other methods also. You can install a program with SCP support [ like WinSCP, FileZilla, etc ] and use it to connect to your servetr. Browse the file once the connection is established and double click on the file, it will open the file in your system in a text editor [ GUI - like notepad ] , you can modify the file and save it.