A little advice needed

[Sneffy-boy]

Hi..I have a pressurised system and wanted to get better pressure from the hot in my shower's..I was told by someone that adjusting the pressure reducing valve would do the trick, then told by another person that I would have to instal a bigger diameter cold inlet pipe to the cylinder, can anyone give me advice on what my options are..
I have been thinking that a better shower may do the trick also..

Thanks..