In order to edit your contacts information, you have to navigate to the list that contains the contact you wish to edit.
Once your on the list, you can use the search field in the top right corner to find the specific contact. The search feature automatically searches all columns of data.
You can choose the quick edit, to quickly change a contacts details by clicking the profile icon to the right. It will open a form to edit from.
Or you can click their e-mail to view all information and data you have for this contact.
Remember to click "Save" once your done.