How can I switch from an agent-supplied retirement visa to a personal retirement visa with my own bank account in Thailand?

@Gary *********

you already have your Thai bank account, so it is very easy to change over, as Brandon mentioned, to what you want to do. The hardest part, and your new passport makes no difference, is getting a Thai bank account on any tourist entry. The type O visa based on retirement is the easiest to get once you are over 50, and have the bt800k in your account. You already have that, as long as the bt800k came from an overseas source. As soon as immigration takes your picture, and fingerprint, on entry, they know everything about you. A new passport doesn't change anything. Just come into the country on any tourist entry, get your two bank letters, and go to immigration and get your new type O for 90 days, then when you have about 30 days left get new bank letters, and anything else they want, and you get your new one year extension. It is pretty simple because you already have your required Thai bank account.

@Gary *********

no. As I said if you leave without a re-entry permit your existing extension will be cancelled.