In your personal account, navigate to Contacts — Your lists.
Navigate to the contact list you want to work with. In the left pane, choose Mailing list operations — Rename.
Enter a new name for your list, and click Save.
Useful links:
Create a Contact List
Delete a Contact List
Copy or Move Contacts Between Lists
See Contact Information & Campaign History
Add Contacts
How to Update Your Contact List
How to Segment Your Contacts