Within 'Manage contacts' in your Message Box account, you will see the 'Find' field along the top panel.
Here you can type in the number, name or any information you have regarding the contact you are searching for. If this information is within any of the fields within your contacts then these will be displayed automatically.
From here you can now edit, move or delete any of your found contacts.
To learn more about managing your contacts. Click the below link