It's quite unnerving to clean it yourself, you need guts and a steady hand in a clean environment. In the inside top where closest towards the hot shoe there is a piece of thin wire like bracket that holds the vew finder glass, got to lift it up to release the catch, the glass will drop and that is the glass you need to clean. Be extra careful though as the glass is very prone to scratches, better if you tape whatever tweezer we are using to lift it out from the camera.
As I said, it is quite unnerving if you have not done this yourself, alternatively, better that you visit your camera service centre and pay them to clean it and another way is ignore it lah since it will not affect your image why bother. If camera still under warranty I believe they will clean it for you, no charge or should I say complimentary.
My advise live with it. After a while you get use to it. If you're really bothered by it get it clean at the service centre. I tried cleaning my camera before ended up scratching the pentaprisim mirror.