Advice sought for basic mods - pls help noobie

[spookz]

I've found the NSW RTA VSI regarding tyres and rims, from what I've read it states the following:
- the outside diameter of the wheel and tyre combination must not be no more than 15mm over the largest diameter combo specified for your vehicle and not more than 15mm less than the smallest diameter combo specified for your vehicle..

Hmm.. I actually couldn't find anything regarding the maximum rim diameter you're allowed to step up to.

It does however state guidelines regarding increase in width of rims.
Rear wheels:
- Vehicles weighing between 801-1200kg, may have a max increase in width of 1.5" over the widest wheel offered for your vehicle.
Front wheels:
- No wider than the maximum allowed for your rear wheels or 8" (e.g. if you have 8.5"+ wide wheels in rear)