If a Role has been assigned to a contact, you cannot delete it
You can rename any Role whether it has been assigned to a Contact or not. To rename a Role, simply click the Edit button as outlined below:
Steps
Select My Apps in the top menu
Select Contacts
Press the More Options button
Select Contact roles
You arrive on the Manage Roles for Contacts page
From here you can
Edit a Contact Role - i.e. rename it
Delete a Contact Role - however you cannot delete a Contact Role if it has been assigned to a contact