More power in a zed is an expensive business.
Probably between 7-15k for a complete install depending if it's supercharged or twin turbo.
If you have thumbs and can do the work yourself, you can get a supercharger kit for about 4k.
You'll probably need an UPREV tune which will cost about £300-400.
The cheapest way to get more power is to sell the zed and get something more powerful.