Shane's right - lots of unknowns here.
Some router bits just can't be sharpened because it changes critical geometry. Most straight bits will be ok, but you may have to take multiple passes to get the width of the cut spot on.
Here in my part of the US (Southwest high desert), it usually isn't cost effective to sharpen router bits.
HOWEVER, first try a good cleaning - soak in a household cleaning solution, brush with a brass brush, dry well and try the bit - often thats all thats needed.
After that, try a small diamond stone such as a DMT diamond sharpener
will sharpen most bits with flat cutters.
If you have a spiral bit, take it to a professional.
Hope some of this helps...