Hi Abdul
CSG is right of course, but, it's not always practicable, and certainly not a cheap option. Assuming you have a conventional system with a copper cylinder and a roof tank, you could have a pump fitted. This would make a great difference to the output. Another choice is to replace your mixing valve with one that has a pump buit in. Check the "Mira" website for details.
If you have a combination (combi) boiler, then the pressure will be mains anyway - with no option to boost it.