Website created in Dreamweaver by someone else and I need to delete it

Your local site folder was likely saved to your computer's hard drive.  Probably something like C:\YourSiteName.  If you wish to delete that, you'll need to do it manually through your operating system's Windows File Explorer or Mac Finder.

To remove Dreamweaver software from your computer, use the Adobe Cleaner Tool below.

https://helpx.adobe.com/creative-cloud/kb/cc-cleaner-tool-installation-problems.html

To transfer a domain name from one server to another, is a bit more involved.  First determine where the domain name was purchased.  Some hosting providers like GoDaddy and Network Solutions also handle domain names.  Log-on to the domain name provider's website, change your DNS settings from old server's IP address to new server's address.  It sometimes takes 24-48 hours to move a domain name.

If you want to take your site down, you'll need to log into your server and delete or overwrite the files that have been uploaded. You don't need Dreamweaver to do that, even if the site was built in DW. You can log into your control panel on your Hosting Company's website and delete the files there.

If you have DW and have defined a site there using your current FTP information...

1. Click Connect (plug icon) in te Files Window
2. Click Expand (2 window icon) in the Files Window
3. On the Remote/Server side of the window, select the files you no longer want available to the public
4. Right Click and Choose Edit > Delete