What should i do with fungus on my lens?

I have a Nikon D90 and its a very new one but i got fungus on the lens after i bought it its a 18mm - 118mm nikkor lens

Added (1). Sorry its a mistake in typing its 18mm to 105mm

Get a new lens. In Photography, cost is irrelevant.

Are you sure its fungus? Fungus usually grows inside the lens and is a result of getting the lens wet and/or storing it in very humid conditions. You might want to take the lens to a real camera shop and get their opinion. Hopefully its just a smudge on the front element and can easily be cleaned. This is why I always suggest a Skylight filter to protect the front element.

Nikon doesn't have an 18-118mm lens. 18-55mm, 18-70mm, 18-105mm, 18-200mm.

If you get fungus on a 18-whatever and it's less than a year old take it back to nikon

As Edwin said are you sure its Fungus? Fungus will be like a transparent to white star shaped growth, once it's got to that stage it's already scrapped the lens, fungus eats glass! Even if you get rid of it (UV kills fungus) it will have 'eaten' into the glass and the lens will flare readily.

Fitting a 'protection' filter will not stop fungus, just the opposite, the still, trapped air between the lens and the filter that rarely gets cleaned is the ideal place for fungus to grow, fungus only thrives in dim, warm and moist (not wet) conditions. If the filter is a UV filter your actually stopping the very thing that can kill or at least slow down the fungal growth.

Here's more on the subject

http://www.chem.helsinki.fi/~toomas/photo/fungus/

For it to be lens fungus as generally understood by everyone when someone says "… My lens has lens fungus… " it would have to have been in dirty or dusty conditions for the slight, tiny bits of dust that are the bedding points of the fungus, and then kept in the dark for many months, if not years, for the fungus to grow. I don't think it's possible for a new lens to suffer so quickly from fungus. If it's a used, badly treated lens you have… It could be anything messing up your lens. Maybe it's not lens fungus but mold from a horrible, nasty, council house. Or something from the sea after a dip in the ocean from the time you went to the seaside and treated the camera really badly.

As previous posted have pointed out fungus usually appears inside the lens on one or more of the internal optical surfaces as the result of damp and is difficult, expensive or impossible to rectify. Is it so bad to degrade image quality? It's usually only a problem if it's near the central axis of your lens so that when it's operating at smaller apertures it obscures most of the light path. If it's not near the central axis you will probably not even notice its effect on image quality.