If you have Windows at home then open Putty and type in “yourUserName@yourDomain.tld” (obviously you need to change that to meet whatever your Shell username and domain are) as the Host Name. Then click “Open.”
Now type your password where you are prompted to do so in the terminal. Note that nothing will show up when you type this. Then press Enter.
You should see something along the lines of “[yourServerName]$” Type in “ls” (that is a lowercase L, not an upercase I, btw) and press enter. That will show you your files.
You probably need some kind of editor installed on your computer. I like Vim. Now, I have never made a custom php.ini file, so I cannot tell you where you need to put it. But I am assuming that it will be fine in your home directory. So you would type “YourEditor php.ini” and press enter. Edit the file and save it (that part will vary depending on the editor you choose).
If you are using a Mac, then all you need to do is open the terminal and type “ssh YourDomain.tld”