You seem to confuse the S-drive with the app SD (Site Designer). The S-drive is a location where your website can be hosted.
If you are OK with coding, you can use the HTML Editor. You can easily open your pages and edit them. Your current code is somewhat old, so maybe you want to start using CSS for the look of your pages?
If you go for SD you would have to recreate your pages, although you'll be able to copy/paste most of the content. It has to be said that most people find that it has a bit of a learning curve to begin with, so making a copy of the files you downloaded from the server is a must, in order to be able to experiment without being afraid of ruining everything.
To make a project of your site, you need to have all the files pertaining to the site in a folder. Then you open the HTML Editor and select My Website, then New Website project. You get a dialogue box where you fill in the name of the project, and then you navigate to the folder that contains all the site files. This is the most important part.
You may also select the upload method. It may be an idea to use the s-drive at first, as a test server, and then you can switch to your real server when you have completed the site.
If anything is unclear, please ask again.
My work in progress:
Components for Site Designer and the HTML Editor: https://mock-up.coffeecup.com