The Contact Settings Tab is where you can manage the Custom Fields that allow you to capture data that is permanent and unique to each contact.
Here's how to Delete a Custom Field:
Contacts Settings - How To Delete A Custom Field - Step 01
Click "Contacts"
Contacts Settings - How To Delete A Custom Field - Step 02
Click the Settings "Setting" icon.
Contacts Settings - How To Delete A Custom Field - Step 03
Click the "Delete" icon next to the Custom Field you wish to delete.