You can update your website using FTP. When you log in with FTP, your username will be ex.gr. mydomain.com, and you will find an empty file "This_is_mydomain.com", and at least 2 subdirectories "www" and "cgi-bin" If you have webmail service you will also have subdirectories "webmail" and "webmail.data"

If instead you see the file "Anonymous_FTP_area" you have not logged in using your username and password, you should log out and start again.

The top file in your website must be called "index" --- specifically the preferred files are:

index.shtml
index.html
index.php
index.htm

in that order. Files ending in ".shtml" are special, and allow you to pull in other files using "server-side includes"

Your www directory is /Sites/com/mydomain/www/ when it is accessed through the web, but /www when accessed through FTP