how do I change members of a group in "people" which replaced "contacts"?

I recently was automatically converted from Contacts to People.  OK, I think all my information was successfully transferred over.  But there was no announcement or offer of instruction on how to use People.  Specifically, I can't figure out how to delete a couple of members of a group.  Members of this group change all the time and I don't want to have to delete the whole group altogether and then create it again with the revised membership list - I just want to be able to add and delete members from time to time.  Help - how do I do that?