To edit a population, click on a population name from the Populations page, then click "Edit Population":
From here, you can hop into the population you'd like to edit and adjust your filters. If you need to edit data sources and/or the associated table - you'll need to create a new population to achieve your desired outcome.
Click "Save & Run" to save any changes to your population.
Quick Editing
Within your main populations page, you can also click ... from the populations page next to the population you want to edit to adjust particular population settings.
From here, you can:
Change your sharing defaults
Duplicate populations
Export
Delete the population
Click "Save Population" to save your changes.