Each library item has a default content type. You can
  change the content type from its default to a more specific
  value.
    This task assumes you are in the library of the desired
    site.
    Where properties are defined for the configured types, you are
    able to enhance the item by augmenting the type (for example, changing a
    standard document to a policy document) and then adding the appropriate
    property for that content type. The property then appears on both the
    details page and the Edit Properties page for that
    content item.
    - Locate and view the content item whose type you want to change.
 - 
        On the details page click Change
        Type.
        
The Change Type dialog box appears.
 - 
        Select the desired type.
        Note: The New Type list remains empty until types are defined by a system administrator.
 - Click OK.