We are considering changing the minimum to open a cd if it is less than 3 years. Most of our accounts are automatically renewed. We will be changing our new account disclosure. Are we required to send a change notice to existing customers?

Only if you are going to require them to meet the minimum deposit amounts at the time of renewal. At that time you would send the full TISA disclosure that is required anyway outlining the new minimum deposit amounts. As a customer service, I would suggest, if they are not going to meet the new minimum deposit amount, then you probably want to also give them instructions on how the redemption process would work.