When you're using your stick for the first time it can be a little tricky to push up because the ingredients are a bit stuck to the tube. So the very first time you push it up it does require a bit more effort, but after that it will slide up and down in its tube easily.
2-3 Millimeters is all you really need to expose, If you accidentally push it up too far just gently tap the base of the tube on a table or ease it back down with the palm of your hand.
Step1, Before applying too much force try holding it in your hands or place the whole stick under your armpit for a minute to warm the tube and soften the deodorant inside a bit :-)
Step2, Lay the closed tube on a flat surface and roll it with the palm of your hand, this should loosen the stick from the tube. You can then steadily push.
Step3, If your stick is particularly stubborn place your tube lid down and press your thumb down on one side of the base circle to get a little movement and then you should be able to push evenly from there :-)