uninstall and reinstall

Uninstalling/reinstalling has nothing to do with your data. To create a new, empty data fileset (empty of accounts/transactions), just do File > New > New Quicken file.

And if you truly wish to 'wuipe the slate clean' (which also implies getting rid of the data which as John says doesn't happen when you do an uninstall/reinstall) and delete all you old Quicken files (after you've backed them up and/or copied needed data), then FILE-->FILE OPERATIONS-->DELETE to get rid of the old Q file sets is a way to clean (most) of your slate.