What documentation is required to extend or convert an O Visa in Thailand?

Okay, if your friend is over 50 and has had ฿800,000 in a Thai Bank he can go to his local immigration office and ask for an extension based on retirement. If he is a non British, US, or Australian citizen and makes over ฿65,000 a month and us over 50, he can get an income letter from his embassy and apply for an extension of stay bases on retirement. If he is married to a Thai or has a resident Thai child, he can with proper documents apply for an extension of stay based on marriage or supporting a child.

If they can't meet the requirements for an in-country yearly extension based on marriage they could go to a thai consulate in Savannakhet Lao or Ho Chi Minh City Vietnam and get a new year-long, multi-entry Non-O visa. Those two consulates don't require any proof of funds to sell those visas based on marriage.

If they are on a year-long, multi-entry Non-O visa based on marriage from a thai consulate (the kind where they bounce out and back in every 90 days) they would need to meet the financial requirements of 400K baht in a thai bank account in their name only for 2 months before they apply for a yearly extension OR they would show proof they have an income of 40K baht a month from overseas.

IF they are wanting to get a yearly extension they should go by their immigration office and get the hand out that lists the documentation and financial requirements needed at that particular office.

You cannot convert an O visa to an O-A.. :/ You would apply for an extension of stay at the immigration office by meeting the requirements for the extension they are wanting

and your friend got the O visa from where and for what reason?