If you have Windows on a BootCamp partition you can boot into Windows from BootCamp directly and Windows should find the update for you and install it. If not you can download the update and install it that way. It should not affect Parallels because it has its own graphics driver that is uses when you boot using Parallels from the Mac side.
If updating this driver does cause strangeness on the Parallels side remove Parallels Tools in Windows (obviously running in Parallels), restart Windows and let it (or force it) to install Parallels Tools. This has helped me 100% of the time that a Windows update or a Windows program install has messed things up.
One more caution. On occasion you will see updates on the PC side to update the firmware of graphics cards, etc. I have only seen these when booting from BootCamp directly (not in Parallels). I have always avoided these for fear that it would mess something up on the Mac side. Usually if there is a firmware issue Apple ultimately publishes their own update, which is perfectly safe to use.