Replaced line of code site now inaccessible

I will preface this by saying I know little about what I am talking about…

I manage a website as a part of my job. Recently, my boss and I were trying to update it, which I have been having problems doing. The site was set up before I started working here and for some reason whenever I want to upload a picture or other type of file I had to upload it through an FTP, which never worked. I was also unable to update the newer versions of WordPress.

My boss was playing around with it and tried to add a single line of code to wp-config.php and replace it in the FTP. When he replaced it, the file size went from whatever number to 0 and now when we try to access the site we get a “Server Error” message and cannot access the site at all.

I don’t know if I’m making any sense but does anyone have any ideas on what I can do to fix this?

Thanks!