You can modify a recipient's information and subscription status manually.
To do so, access your list and click on Manage subscribers on the left hand menu. Click on the subscriber you wish to modify, and on the next page click on the Edit button.
You may change all fields except for Sign Up Date.
If you wish to unsubscribe the recipient, click on Unsubscribe this recipient on the left hand menu.
MODIFY A GROUP OF RECIPIENTS' INFORMATION
You can also modify a group of recipients' information by downloading the contact list and making the changes within the CSV. Once completed, delete the system-generated fields and all other unnecessary fields except for the email field. If you want to add another field, you may do so - just remember to map it when prompted while uploading. Proceed to re-upload the new-version of the CSV to the same contact list.