Some controllers may require the latest available firmware in order to be compatible with Serato DJ. 

Click here, then select your controller to check if firmware are required. If they are required, there will be an available "Download Latest Firmware" button. This button will then take you to the hardware manufacturers website where you access the latest available firmware.

If there is no "Download Latest Firmware" button available for your controller, this means that there is no necessary firmware update required.

NOTE: Sometimes drivers are required for Windows only, but not necessary for Mac.