if your talking about the ones on the front theres one bolt holding the corner piece in, unbolt it, slide the corner out and you have easy access to the bulb
I'm not in front of the stang right now but the first thing you need to do is take that big black plastic cover out of there. I'm talking about the cover on top of the radiator. It also blocks the access to those corner lights. Then you'll see the bolt/bolts (not sure..) that holds the corner light. Then tap it a little bit to take it out.