There are a few different ways to remove the flow restrictor from your shower head, depending on the model that you have. The most common way is to unscrew the shower head from the hose, then remove the washer and o-ring before reaching in and removing the flow restrictor. Another way is to use a small pair of pliers or needle-nose tweezers to remove the flow restrictor.
Image Credit: https://showeradvise.com/