I have a 06 cobalt should be exactly the same
fold down the seats, look at the headrests, pull off the plastic covers where the two pieces of metal go into the rear deck, there should be 2 bolts in these just loosen them and slide the head rests out.

Then look at the pillars by the window there are plastic caps near the middle of the pillar, pop these off and underneith there will be a hex screw undo what and carefully pry those off then I believe that the only thing stopping you from pulling the rear deck off the car is 2 clips which slide out wwhen you pull it up, seatbelts will still be attached to the rear deck though, I just worked around it