Whether it has the oil on the lenses since you say it is dirty now, you can add little amount of cleaning agent with water to wash it. Or else,you just use the clean water to wash the lenses of serengeti sunglasses and use the clean cloth to dry the lenses.
Well, to clean the serengeti sunglasses, you should follow some steps. For example, if the lens is merely dirty and not covered in abundant grease and grim, you can use a good quality linen or cotton cloth which will work wonders. Then, you can also use some resolution to clean it one more time. For the surface of the nose pad, you can also soak them for a couple of hours in warm water to loosen the residue. Then it will be easy to gently brush away the unwanted dirt with an old soft bristle brush or old toothbrush. Anyway, you should do the entire task in a gentle way so that you will not damage your sunglasses.
Be sure not to wipe your sunglasses a wiping rag directly in that most glasses are made with the resin which has low resistance to wear. Direct friction will scratch lenses. When your sunglasses are dirty, you'd better rinse them under running water and then dry the lenses with tissue carefully. If washing them only by water doesn't work, you can clean them with a little cleanser essence. Besides,knowledge about how to maintain sunglasses is also necessary for you. For example, cleaning sunglasses after wearing is important for metal parts of the frame are easy to be corroded by sweat or grease on the skin , so daily cleaning of sunglasses is helpful to extend the period of use. And don't put sunglasses in the sun when you don't wear them.