some games run on dx 11 and some run n dx 12 and sme old ones still run on dx 9. each is separate from the others so it is likely you have multiple versions installed. this is normal.
as noted above, if you do not have win 10, then you can't use dx 12. if you have win 10, then you have dx 12 but it may not be used in many games you have. it is slowly being adopted but not available on every game by a long shot