How do I pump up water pressure in my shower?
I would start with new Shower head. You make have a low pressure model or it may just be clogged/hardwater build up.  If that doesn't work check your water filter it may be clogged and needs to be replaced. Many have a bypass so you can see if there is any difference. It is possible you have partially clogged pipes or your shower cartridge/valve  could be blocked with dirt in the screen.  You can replace the Pressure Switch with a 40/60 psi.