Who owns the digital copy of your trust? If I change lawyers can I take the digital copy to the new lawyer in case of future changes in the trust?

You own your entire file (digital or otherwise).  You can go to any attorney you like whenever you want. You don't have to tell the former attorney but it's probably a good idea. In California the attorney you leave can not charge you to copy your file or any other charge either. If they want a copy they have to pay for it. Do your research and find someone that truly specializes in wills and trusts and not just someone that dabbles in it. Good luck.