You can change manually the ownership of a contact at any time.
As a manager you can operate on all contacts, and as a user only on contacts you already own.
To change the ownership:
1. Go to the Contact view and select the contact(s)
2. Click on 'Actions' and then on 'Change ownership'
3. A window appears:
4. Select the name of the user (with the picklist) who will become the new owner and Submit
By default, the contacts's owner is the user who created it or the last user who added it to a sequence.