Hi PIXX,
A fungus infested lens can easily be identified by holding it against a light source and look through the glass. If the infestation is severe enough, you might see spider crawling inside... joking ! But you will see cobweb like, whitish/yellowish/bronwnish growth somewhere in the lens. Sometimes the growth might be so severe that it covers the whole lens surface.
Cleaning of lens fungus beyond the front and rear surfaces will require dismantling of the lens. You will probably need certain special tools like rubber bunk and lens wrench to dismantle the lens. Cheaper modern electronic AF lenses might be worse as some with barrels made of plastic and the assembly might be a permanent one with no option for dismantling.
Putting it back is another challenge, especially on those zoom lenses. Hence I do not recommend such action unless the lens is to be junked anyway, and you would like to see how a camera lens is like beyond the aperture and focussing rings. It's better to leave it to the professionals for a valuable lens.
Hope this helps.
e905591s