Since you will be draining some of the water first there is no pressure to worry about. Shut off the water supply (for a shower, it usually means you need to shut off the water at the meter) and open the shower valves (hot & cold, if applicable) then find a sink, toilet or outdoor water faucet at some level below the height of the items you are to replace. You don't have to open them for long... a few seconds will do. This allows air to enter the shower valves and pipes and will drain to a point so that dripping water will not be a problem.
Open up the actual shower head and remove the factory fitted restrictor.
Replacing an old or unwanted shower head is usually as easy as unscrewing the current head and replacing it with your new shower head. Simply screw the new shower head on and tighten it with pliers.
It is possible that a piece of the rubber washer or some material has slightly plugged it in the diverter.
pressure and humidity
This does vary slightly according to the shower, but for a shower without a pump, using a gravity feed, a water pressure of at least 0.1 bar is recommended. If your water pressure is low you will need to install a pumped shower.
If the pressure problem is in the shower try removing the shower head but leave the shower arm in place. Then turn the water on and see if you have a good flow of water with no shower head in place. Sometimes the shower head gets clogged with a mineral deposit which needs to be disloved with something like CLR (brand name). Some bath faucets have a screen which can be unscrewed and cleaned as well but his is rare. If thhese checks do not help you will probably need a plumber to check if there is anything that can be done such as replacing pipes which may be clogged with deposts.
A leaking shower valve by installing a new cartridge.
The flow of water from the shower creates a low-pressure area inside the shower stall, causing the shower curtain to be drawn inward due to the difference in pressure between the inside and outside of the shower. This phenomenon is called the Bernoulli principle, where higher speed of a fluid (in this case, the water spray) results in lower pressure.
The simplest and lowest cost solution is to replace the shower head with one designed to increase the pressure.
The downward movement of the water in the shower creates downward movement in the air inside the shower area. Air flow causes low pressure and so the air pressure from outside the shower area is able to push the curtain inwards.
You would use it to deliver a constant pressure at the shower-head, in situations where the water pressure is either low, or fluctuates.
The company Oxygenics makes shower parts. Some of the products are shower heads, self pressurizing shower heads, pressure shower heads and shower fixtures.