There is a 32 bit and a 64 bit version of a Fanatec driver available. It depends on the "system type" of your PC which of those versions you need to choose. If the system type of your PC has a 32 bit operation system, you need the 32 bit version of the driver. If the system type of your PC has the 64 bit operation system, you will need the 64 bit version.

For finding this information go to the "Control Panel" of your PC -> "System and Security" -> System: