Well it's actually very simple all you gotta do is place a portal on the wall and then another portal above it and be sure that the turret is aiming at you so that after you move a bit it will hit GLADoS

After that you gotta use physics with portals so that you get a lot of momentum in order to get all the personality cores that glados dropped/stayed in the air

After that simply place a portal near the button and then one near the incinerator

Do that fast and 4 times and good job you killed this annoying robot that lies about cake

See Ya In Portal 2!

(You after)