but it's not adviseable. It may leave folders lying about that have slightly different names, and this will confuse you even more.
If I were you I would download a free FTP client such as Filezilla or SmartFTP and delete everything that you have up there. Then upload the new site.
If you are a bit nervous, you can always use the FTP to download the existing site to your hard drive until you are certain the other one is OK.
Good luck, Whiz....