Matty pretty much explained everything, but to break it down:
1. go to
www.nvidia.com and download the latest drivers (which you did, apparently)
2. install the drivers (they should be in your download folder, just double click on them and go through the wizard)
3. after you installed them, restart your pc (it will ask you to do so anyway)
4. when it's running again, right click on your desktop and select "NVIDIA Control Panel"
5. in there, check on the left side bar for a voice saying "Manage 3D settings" or something like that, click on it
6. In the window that opens there's a drop down menu, where the games installed on your PC are listed
7. select the game from that list, WoW should be there already
(7a. if WoW is not in the list, click on the button that says "Browse..." and navigate to your WoW installation folder)
(7b. select the executable file of WoW, the one that ends with .exe, just be sure you're selecting the game .exe and not the launcher, i'm not familiar with WoW but I'm assuming you might have something like wow.exe and wowlauncher.exe. If you dont find browse in the subfolder, that has to be there somewhere)
8. once the game is loaded in the list, in the drop down menu below it, you have 3 options that basically say "use default settings", "use nvidia card" (this one should have a green nvidia logo on the left side of the label) and "use integrated card".
9. select "use nvidia card" and hit apply+ok
10. close it and play the game, that should fix it.