You can delete populations from the edit population page. Click the trash icon next to your population builder on the bottom left of the page. You will be prompted before the population is deleted, including a warning that deleting the population will remove any associated data sharing rules. Click "Yes, Continue" to delete the population.
Population deletion cannot be undone, so be sure you want to delete your population once you hit "Yes, Continue".
You can also delete a population within your main Populations page, using our quick edit filtering next to an individual population.