First go to the entrance to the computer room in summit from the cable car.

Look to the left towards the closest computer, climb on top of it and look toward the entrance.

If you look to the right and up you'll see a walkway. You can jump on the walkway by jumping and pressing A to climb over the fence.

After that look to the left and youll see a window. Just out side it there'll be a tower.

Knife the window, run and jump and press A to climb on the fence of the tower.