You will only have access to this option to edit contacts if you are a Manager or Supervisor. Member users cannot edit other users.
On the App home page, click on the menu in the upper right corner:
Select the "Users:
A list like this will appear below, displaying all users within your company's Biptt environment. The dark blue color with the star represents who is allowed to manage other users as well.
To edit a contact, change your permissions or delete it, just click on the name and choose what you want to do from the options below.