If you wanted higher spring rates, you could order slightly stiffer spring rates but I would not go up more than 2kg in spring rating without potentially causing harm to the shocks and causing a premature shock blowout.
In general, We do not advise changing the springs without changing the shocks as well because the shocks that come on the kit are valved for the certain spring rate that comes with the kit, and changing it can cause the shock to prematurely blow which will not be covered under warranty. When you have too much spring rate the car will be harsh riding and will begin to understeer/oversteer sooner. It might feel very responsive and feel like it “handles” better, but ultimately you’ve made the car less capable
The rear shocks more importantly are not valved for crazy stiff springs and this would mess up the ride quality and could very well blow the shocks.
If you are certain about changing your spring rates, you may, but you will have to obtain the springs separately from this link:
It is a universal listing so it will ask you to fill out the information about your vehicle, the kit, and when the kit was purchased so we know what springs need to be ordered. Please note that some springs we have in stock and others are specially ordered for about 4-6 weeks.
The springs vary in mm length (270, 250, 235, 215, 205, 185, 180, 160, 150, 140) so we suggest measuring them before ordering. You could also take a look at the printed white markings on your springs. These numbers are going to be the wire diameter and the spring length in mm, for example, 13-180 means it is a 13mm thick wire and is 180mm long, then look for the appropriate spring lengths and proper spring rates over the replacement springs section.