This only affects Knowledge Center, as there are no differences between a Standard and Professional installation of Developer. This is an "upgrade" from Standard to Professional using the same version, and not an upgrade to a newer version.
To convert a Standard Installation to a Professional Installation:
Run the installer from a media pack licensed for Professional.
On the Setup Type screen, choose the Knowledge Center installation type.
When you are prompted for the installation location, if you are on the same machine as the Standard installation, choose the location where Knowledge Center is already installed and confirm you want to overwrite the existing installation. If you are not on the same machine as the Standard installation, select a new installation location.
When you are prompted for the web site and virtual directories, if you are on the same machine as the Standard installation, choose the same web site and virtual directories and confirm that you want to replace the existing virtual directories. If you are not on the same machine as the Standard installation, choose the web site and virtual directories you want for installation.
When you are prompted for the database information, indicate that the SQL scripts have already been run. Select the same database server and the same schema (on Oracle Database) or same database, user name and password (on Microsoft SQL Server) where the Standard installation database was created, and confirm that you want to use that schema or database when prompted.
To convert a Standard Installation to a Professional Installation: