You should have access to your web host via an ftp (file transfer protocol) address. e.g.
ftp://mysite.com. You should be able to find out what the address is from your CPanel. If you cannot, then simply go to the page you want to edit and click File>Save As and save the document to your PC, then open the file with dreamweaver.
If your site uses an external .CSS document to style it then while you are editing on your pc you may notice it looks slightly odd or different, but it will be back to normal once you upload it again to your host and view it overnet.
If you want more detailed advice but do not want to give out too much detail in the main forum then PM me.