How can I edit contact details?

The matter details screen shows the different contacts captured on the matter:

But you cannot edit them here - to add/edit contacts and contact details you need to open the client intake form:

And then go to the contact details section (or however you may have renamed that):

One thing to note - in the contact details section the client can delete contacts (other than themselves) up until the point they submit the questionnaire. After submission, only the attorney is able to delete