There is no direct way to clear all statistics, but you can start fresh (even on the same URL) by following these instructions:
- Unhost the landing page (remove the URL from the Publish tab) and Save.
- Create a duplicate of the landing page by selecting it on the main Landing Pages screen and then choosing "Copy" from the action menu
- Rename and rehost the copied page on the URL desired. The statistics will be at zero for this new page, even if on the same URL.