Nibal,

Generally speaking, you have two main factors that come into play when you are doing an irrigation design: Pressure and Flow.

Pressure can be altered in a few ways if you have exceeded what you have at your point of connection (pump, change speed of water, change design pressure of your equipment). Flow, however, is pretty set given the size of your point of connection. This is why your only real option is splitting the zones up until each zone falls under what you have at your source.

I would say you could change your equipment to handle more flow (larger valves), but the problem still is that you just don't have that flow to give that equipment.

Use our circuiting tools to run a flow total (which will help you understand the minimum valves you will need) then break the design into smaller zones. Once you place the circuit zones around the different areas, use the circuiting schedule to see that you have evenly split those zones to minimize how many zones you will really need.

From there you can use the delete station tools to remove the pipe from the old zones and simply repipe to match your newly circuited zones. 

I have listed a few links that should help with the understanding of this process.

Power Tip: Circuiting

Circuiting and Zones