I have one of the first device to connect any TV to Roku and it was setup with an old email that I no longer have.
How can I access it to update my email?
I also have a new Roku TV that I created an account for. Can I reprogram it to that account?
Does it involve a total reset and setup again to happen?
The answer to your last question is "yes" - you have to factory reset a Roku device to change the account. However, depending on how old your Roku device is, you may not be able to complete the process. It's been reported that devices that are considered "legacy" devices and are no longer receiving updates can't be activated. If the model number displayed under Settings->System->About is on the list in the following link under "Legacy models" you may not be able to activate it again, but those devices are also becoming more and more useless due to not being able to support many current apps.
Hardware specifications | Roku Developer
You didn't necessarily need to create a new account. You can change the email used for an account, and the devices will update. I have done that before.
But since Roku added the email-based 2FA requirement (which you can turn off), you may not be able to get into that old account in the first place.
Otherwise, you can try to follow into information that @renojim posted.