Help with accessing a website creating with Homesite

If you know your server's log-in credentials, use free FileZilla FTP client to connect and transfer files to/from your server.  

https://filezilla-project.org/download.php

Once you have the remote files on your computer, you can use any decent code editor to make changes.

=============
CODE EDITORS:
-- Adobe Dreamweaver CC - https://www.adobe.com/products/dreamweaver.html
-- Codespaces (free, browser-based) - https://github.com/features/codespaces
-- Nova (Mac only, formerly called Coda) - https://nova.app/
-- Pinegrow - https://pinegrow.com/
-- Sublime Text - http://www.sublimetext.com/
-- Visual Studio Code (free) - https://code.visualstudio.com/

That said, a 13 year old site created with obsolete software from the 1990's is unlikely to be fit for modern use.  Current browsers and  mobile devices will probably choke on it for various reasons.  There's little point in postponing the inevitable.  You'll need to build a new, responsive site with modern code & software.

Start here:

Read chapters, do code exercises and take quizzes at the end.
- https://www.w3schools.com/html/
- https://www.w3schools.com/css/
- https://www.w3schools.com/js/
- - https://www.w3schools.com/bootstrap/

Hope that helps.