Personally I would not bother with any version of this radio if you are using it for offroad.

But here is the version info you asked for

V1 is the initial release of the radio

V2 is a main unit update that was supposed to make the radio have a more linear throttle feel

V3 is a V2 main unit and a new V3 Grip.

In order to go from V1 to V3 you need to send in your V1 Main unit and if you send it to the US office it needs to be a US serial number, if its a Japan Serial you will need to send it to Japan, then, IF KO has updates in stock KO will update you for a fee. Add $100 ish for a the V3 grip the grip has an adjusted trigger and and different contour on the grip.