An EXIF or IPTC editor will accomplish this task. You can use one of many simple apps for this and most photo editors include the capability to make these edits. Windows, since version 7, includes an IPTC edit capability in the file browser (see Windows 7 Explorer). Using a Mac you need to add an app even though you can display the IPTC data in finder.
Note: For Windows 7, the IPC editing capability is available in File Explorer (see screenshot below). Also note, that the IPC data is embedded directly with the file, not as a separate file. The file extension for the IPC data is .IFO. To use this file editing capability, launch File Explorer (see picture below). Click on a file with IPC data that you want to change. Then click “File Information” tab. In the field labeled “File Information” you will see “I/O Stream (or I/O Stream Address)” for the original file. This information is used to identify which I/O stream you must input to get the I/O stream address. As I explained in my tutorial on I/O stream identification, you must enter that address when you edit the file. You must be careful to only select one of the input files to edit, not both. In the dialog box you will.