In order to be able to change a contact, search for the desired contact and select it with your mouse, to get to the detailed view. There you use the Edit button
to switch to the editing mode. The button is only visible to you if you have suitable write access. You can now change either the permissions or the details for the contact. The display of the form corresponds to the form that you also use for entering a new contact.
To save the changes, confirm the form by clicking the Save button. If you decide not to save these changes, you can leave the menu again by clicking on the Cancel button.