If you you really want to start over you don't need to uninstall Money. Just open Money and then select File>New>New file. Give it a name that is different from your current file and you will have a new empty file.
But before you do that, have a look at Banking>Account Tools>Categories and Payees>Payee Rules Manager. That will allow you to tell Money which phrases and words to ignore when they occur in downloaded transactions and how it should rename
(or not rename) payees in downloaded transactions.
Bill Becker