Alex 1986, the reason why you are not able to install the graphics drivers could be because the systems manufacture, in this case Dell, is not letting you do it.
Bear in mind that we provided generic drivers; therefore sometimes these cannot be installed on Dell systems or the installation of them would overwrite Dell customizations and possibly change the functionality of the graphics, but you can give it try. I would recommend using Dell’s graphics drivers.
If you are still want to install our drivers, you may try forcing the installation by performing manual procedure, however I cannot assure you they are going to work as expected. See here for instructions: Graphics Drivers — Computer Manufacturer Graphics Driver Detected
The following link will show you the list of drivers available for your system, please choose the operating system you are using and download the latest version available. Then try the manual procedure.