How do I delete audiences I created? Can I delete several at once?

Yes. In the progress list, each audience you created has a trash button for deleting it individually and a checkbox on the left. To delete in bulk, select the audiences you want (hold Shift and click to select a range, or use Select All) and click Delete Selected. A confirmation window appears first, because the deletion happens directly in your Meta account and can't be undone. Important: Meta may refuse to delete an audience that an active ad set is using. In that case, the error message explains why, and you need to remove the audience from those ad sets first.