Many actors/actresses change their names from ethnic names to " American " names so they can be more easily accepted, or do to prejudice real or perceived.
Many of the actors from the 1930's-1960's changed their names do to the anti-semitism that was rampant in the US at the time
People still do it today for similar reasons although it is not as common as it used to be.
Some also change their names because they supposedly want to succeed on their own, even though their is a huge family connection in the business. Although they would not even have the opportunity to be in the business if it wasn't for the family.
There are a couple of reasons why people who are actors/actresses change their names. They want a name that is easy to remember and is marketable. The other is if they have a common name, the Screen Actor's Guild does not allow a member to have the same name as someone else.