You have not followed the upgrade instructions in the upgrade folder.
You need to upload ALL FILES except your config file, any modified stylesheet if you modified one and of course the header.htm footer.htm
So in essense do this
Unzip the files to your computer.
Delete the following files
/stylesheets/default.css --SINCE YOU MODIFIED THIS ONE
UPLOAD EVERYTHING ELSE OVER YOUR CURRENT INSTALL ON THE WEB.