L4D missing eye texture

Hey guys, I got L4d and gmod and have seem some tutorials of how to import l4d models/materials to gmod and it worked fine except of the survivors that got no textures on eye
so i’ve seen some tutorials of how to fix this they say to change the directx level to 90 well the problem is HOW I CHANGE THE DIRECTX LEVEL TO 90 ?

OBS.:Whatever you say this is a moved copy of my other thread.