How can I edit, reset or even delete an audiences I have created?

Reset Audience: From the audience dropdown menu, select the desired audience and click on 'Clear all' next to the 'Apply' button. You can then update the filters and save the audience again.

Edit / Delete Audience: Choose the audience you wish to edit/delete from the dropdown menu, click on the icon next to it and select the option to edit/delete the chosen audience. You can even duplicate an audience which might be useful if various filters were selected and only a subset needs to be changed for a new audience.