Can a plumber give me a simple answer to what I think is a simple question?

I'm working with a building in Thailand to improve the water supply.
Currently we have a pump and pressure tank that can just get up to 2.5Kg/cm
(2.5 bar). This pressure is just enough. Problem is when it reaches pressure
it switches off and only comes back at 1.7 bar, not enough for most rooms.
So we get a varying water supply from a trickle to a surge. If we leave the
pump on continuously we use far too much electricity.

We have a lovely electric pump, 8 amp so plenty of power, and a header tank
4 metres above the pump.

Can I just change the water pump part - is that the impeller?

If I change it for a pump that can get up to 3.5 bar is that the same as a
pump that can give a 35m lift?

Thanks,

--
Mark BR