Removing screws off of T420 and T430

Hello ! I bought 2 T430 and T420 off of my local marketplace and I'd like to open them to upgrade them, but the screws are really REALLY tight. I tried with a rubber band but didn't managed to pull out most of the screws. I'm really weak and I really can't manage to pull them out no matter how much pressure do I put on top of them and I'm pretty sure I'll just damage the screws if I continue to force like this. Does anyone have tips ? None of them are too damaged for now