Hi shahar,
Welcome to
RP!
To remove/reduce grain/noise from a picture, you could try this excellent
Tutorial by Vikki...
If the grain/noise is very strong, you could try this other
Tutorial ... If you are still not happy with the result, you could post the picture, or part of it, and somebody will give you specific advice.
If you don't know yet how to post a picture here, just follow the links below my signature and you'll find step-by-step instructions.