What documents are needed to change a Non-O marriage visa to a Non-O retirement visa in Thailand?

You have to look, that you have 2 months prior application for your EOS, 800k on your bank account (instead 400k for mariage).

After you need to maintain 800k during 3 months and after not drop under 400k.

I am doubtful you're actually on ANY Non-Imm visa 😮

It's far more probable you're on a yearly extension based on marriage to a thai that you got from the immigration office, look at your current stamp and see if it says "extension of stay permitted until" and has a date. If it does you're NOT here on a Non-O anything you're here on an extension FROM an original Non-O

If you are changing from marriage extension to retirement extension when your next extension is due you just need to get the documentation together and apply for retirement not marriage this next time

OR

If you're changing the reason because you're getting divorced you can go early and cancel your current extension and apply for a new one based on retirement right then

You should GO to your office and get the hand out they have listing what the requirements are at the office you use.

This is a GENERAL list of the requirements for a retirement extension it is not office specific.