Increasing water pressure in your shower means making the water come out of your showerhead faster and stronger. To do this, you need to first make sure that your pipes have enough water in them. If they don't, then you need to check with your plumber to make sure they are big enough to carry the right amount of water to your shower.
Once you know your pipes are the right size, you can increase your water pressure by adding a booster pump. This pump will push the water through the pipes faster, giving you more water pressure in your shower. You can also replace your showerhead with one that is designed to increase water pressure. This will give you more water pressure in your shower without having to add a booster pump.