I want to change my will written in December of 2002, should I write a new will or amend it and is a codicil necessary?

The choice is yours. It may depend on if you are using the same attorney or a new attorney. It may depend on how much information you are changing. Today though with technology, an attorney is likely to write a new will for you as opposed to a codicil. Your attorney will help you decide what is best for you.