FTP is used to send files TO and FROM your server. After a program is successfully installed on the server, you should create a FULL BACKUP COPY of the folders and files on your home machine. And you would use FTP to copy these across.
Then, when you have a COPY of all your files, you should get into the habit of editing a LOCAL file (ie: one on your hard drive), backing up its counterpart on the server, then sending the edited copy to the server to occupy the same location as the original.
So... if it is necessary to edit: includes/languages/english/CUSTOM_TEMPLATE/english.php
... you will go to this file on your HOME computer.
You will edit this LOCAL file.
Then, on the SERVER (remote file), you will navigate to the identical location: includes/languages/english/CUSTOM_TEMPLATE/english.php
... and you will RE-NAME the file:
includes/languages/english/CUSTOM_TEMPLATE/english.BAK
Then, you will ftp your LOCAL file:
includes/languages/english/CUSTOM_TEMPLATE/english.php
... to the server, so that it is in the SAME FOLDER (directory) as:
includes/languages/english/CUSTOM_TEMPLATE/english.BAK
In this way, you do NOT edit the file on the server, but by calling it english.BAK, you protect it. If your locally edited file english.php is faulty, you can delete it from the server, and just change english.BAK to english.php again...
Then try again, correcting any mistakes you made the first time.