Obviously you don't have Win7.
Since you downloaded DX11 you should be able to un-install it in add/remove programs.
Your O/S will have either DX9 or 10.1 natively depending if it's XP or i assume Vista.
Run this once you un-install DX11. http://www.microsoft.com/downloads/en/details.aspx?Fami...
if you only have xp then directx will only install dx9.c components. it wont install dx11/ although the dxdiag will tell you that you have dx11 on your system.
you shouldn't have to uninstall anything. just run a dx redist installer and it will update any missing components.