I'm assuming you use Boinc for the IBM World Community grid. Log in on the World Community Grid Homepage https://secure.worldcommunitygrid.org/index.jsp in the top right corner of the screen you will see "settings" click that. On the next page that pops up you will see "device manager" -> "device profiles" click on your registered device and you will be able to change the profile for the device by clicking "Edit Device Profiles" and assigning it to your machine.
Take a look around and feel free to ask if you have any more questions.