There are two ways to modify a file on the server using FileZilla.
- You can of course alter it locally, and then transfer it to the server again. FileZilla will promp a window asking if you want to overwrite the file, or skip the file. Choose overwrite and it will overwrite the old file with the new one.
- You can locate the file on the right side (server side) and right click on the file. This gives you a few options but you are currently only interested in view/edit. This opens the files in your default text editor. From here you can edit the file like you normally would. When you choose to save, FileZilla will promp a window asking if you want to upload this "new files" (Edited file) to the server. Hit yes and FileZilla will overwrite the old file with the new file.
Both processes executes the same function of overwriting. So you have to choose which one you is most suited for you. Neither one is better then the other.