How can I increase my water pressure in upstairs bathroom?

Call a Plumber...........

Do you know what kind of pipes you have? If its an older house and the pipes are metal, there could be buildup slowing down the flow of water. If that is the case, its best to replace those pipes. A plumber would be the best course of action

Clean lime out of faucet perhaps, or replace screens in tip of faucet

The key to deciding where to start often is on how long the pressure, / flow has been an issue. Often dirt, silt, ect can come from repairs on the line, or water main. Rust from flushing lines can add to this, as can lime build up.

All these can often. can be corrected by removing faucet and shower heads, screens and filters and cleaning or replacing them.

One problem in solving it is not understanding the actual problem. Is it actually an output flow issues or loss of pressure??? flow.. (ie slow) is what we see.. pressure is a bit diferant,.. an example is a garden hose, if you reduce the nozzle opening size by placing a finger over it, it sprays harder.. ( the outlet pressure increases. ) By reducing the outlet diameter, it gives you give the appearance of an increase in pressure.. (flows harder and faster). Just as a larger outlet pipe appears to reduce the pressure.. it gurgles out the end much slower and with no real force. (when in reality, the actual pressure in the hose/pipe stays the same. )

The solution may be as simple as reducing the outlet heads once you have cleaned as much lines silt and deposits from the pipe ends to water saving heads. On a newer home or remodel it may require you adjusting the flow regulators. hope this helps you find a solution.

https://trustedbeasts.com/best-high-pressure-shower-heads-low-water-pressure/

there are pumps