It’s easier to do a new install. With SSH access to your 1and1 account, here’s what I do (using the existing MySQL db which will be scratched).
1) Rename the directory (just in case I want it back)
2) Make another directory with the original name (the directory that your 1&1 domain is pointing to)
3) ftp the Joomla zip file to the root directory and un-zip it.
4) Browse to the URL and follow the normal installation instructions (see my blog entry on that) except that on the Database Configuration page, select the Delete existing tables option in the Advanced Settings.