On Windows XP, Vista or 7, a Touchpad tab in the Control Panel features settings and a toggle with which to deactivate the touchpad. On Windows 8.1 or 10, a similar toggle providing the option to disable the touchpad is found within PC Settings under PC and Devices.
Make sure the latest touchpad drivers are installed to ensure access to the touchpad's settings. These drivers can be found in the Mouse, Keyboard and Input section. If they're not installed, download them directly from Dell. Windows 8.1 and 10 operate differently than older iterations; Computer settings can be found in the Charms Bar on 8.1, and it's best to simply search "touchpad" on Windows 10.