Well, if the laptop has buttons for adjusting these values, it should say in the manual.
You can check the display properties and adjust them.
Right-click on the desktop, go to properties. Go to the Settings tab, then 'Advanced'. If there's GPU specific drivers installed, you should see a tab for the particular GPU used in the system. While it varies from GPU manufacturer to manufacturer, poke around there and you should find some settings for brightness and contrast.