When this happens, access the Start menu and begin typing View devices and printers. Open the section, select the printer you want to make the default one, right click it and choose Default. Restart the Memorex exPressit Label Design Studio software and then access the Print function.
While in the Control Panel, you can put the other devices offline to force Memorex use only the one you want. I've just tested this with another application and it works properly.