The BIOS entry is also called SETUP Reanne so you need to press F2 on your particular pc.
Once you get the BIOS screen up you need to go through the menus, the one you probably want will be called Advanced or Integrated or similar although some BIOS do have different things in different pages and different types of pages.
You want to look for something like Onboard Graphics or Integrated Graphics and disable it.
There will be instructions at the bottom of the screen for how to alter the settings, usually you use the up and down arrow keys to highlight the item you want to change then sometimes its press Enter to open a submenu and others use the Page Up and Page Down keys where others use the + and - keys to change values.
Once you make any changes in BIOS its alwys a good idea to write them down so you can change them back if something doesnt work as it should afterwards.
Dont forget to select save changes and exit as you leave the BIOS otherwise it wont change anything when it restarts
Sorry Simon, I didnt read what you wrote as being the same as I did or mentioning the disable in BIOS part to stop conflicts between the onboard GFX and the newly added one :?