I have white filling on my teeth, how can i make them whiter?

White fillings: You cannot whiten composite restorations (fillings). In fact, if you whiten your teeth, the composite fillings will appear even darker. My advice-- first whiten your teeth, wait a couple of weeks for the shading to settle, then replace the dark fillings with new restorations. This is all optional cosmetic dentistry, assuming the dark fillings are functional.

Replace them: You may try to have them polished to remove surface stain. However they can change color over time due to what you eat and drink, habits, etc. Bleaching will not have much affect on resins and porcelain. It will make them appear dark, more contrast. Replacing them with new bonded resin material is the best option you have for whiter smile.