FortiWifi 40C Configuration - Multiple subnets best practice

[CanterburyComputers]

Apologies if this is the wrong section.

I have a FortiWifi 40C and wish to split my network in to a number of subnets, one for internal systems and others for customers with potentially virus ridden machines!

Firmware :

Operation ModeNAT [link=https://192.168.10.254:4443/p/system/vdom/root/][Change][/link]System TimeTue Nov 15 10:56:39 2016 (ntp1.fortinet.net) [link=https://192.168.10.254:4443/system/config/settime][Change][/link]Firmware Version

v5.2.9,build736 (GA) [link=https://192.168.10.254:4443/ng/#/system/firmware/][Update][/link]

Using the gui interface I can't find a way to achieve this, is it a CLI only function?

Is it possible to setup the five internal ports on the device as separate subnets? What is the best method of doing this? 

If this solution is not feasible are there any other methods of achieving my goal?

Thanks

Paul