It's there, you're not looking hard enough. Assuming this is for a Kenwood Music Keg:
1. Put your DMS in the USB cradle and start up PMM, then connect to the DMS.
2. Press the Hardware Options button, over to the right side of the screen in PMM. This will bring up the Hardware Options window.
3. The first tab is Firmware Setup. Press the Properties button. This will bring up the Modify Firmware Properties window.
4. Under Firmware Properties, click on List Title Text. Change the Value of Firmware Property to Disc Text.
5. Save changes, and then save/eject DMS. Done.