Cant get headlight cover off to check space for LED's

I'm trying to remove the back headlight cover to see how much space there is for LED's headlight.

Just getting my big hands in the gap is a issue. The cap turns really hard. I'm about a cm away from aligning the 2 arrows, but just cant get it to turn the last bit. 

I need to get it off so i can know which LED's to buy.

Has anyone fitted LED headlights to their S10 and can help met with what to get and how much space is available?