Is it worth replacing my amalgam fillings with white ones?

It is usually best to change fillings only when your dentist decides that an old filling needs replacing.  If so you can ask to have it replaced in a tooth-coloured material.

Some dentists prefer not to put white fillings in back teeth, as they are not always successful.  One way around this would be to use crowns or inlays, but this can mean removing more of the tooth and can be more expensive.