In laptops the gpu is onboard in like 99% of the time. Only the fancy gamer systems like the alienwares had removable video cards.
The only real way to know for sure is to find an exploded diagram of the computer on the manufacturers site. Dell often provides really great manuals to thier computers.
Are you looking to upgrade the gpu or is it defective and in need of repair/replace, or are you looking to update the drivers