What is the process to change a 30-day tourist visa to a marriage and dependent visa in Thailand?

Hi guys.

I have just arrived on a normal 30 day tourist visa.

I am looking to change this to a visa based on marriage and dependents (married with 2 kids).

What would be the initial step that needs to be done in order to process the visa I require. Hell I don’t even know the name/number of the visa.

All I know is I must have 400k thb in the bank (the money is there albeit in a foreign current deposit account, and has been for years) with a Thai bank.

Can you let me know what documents would be needed and where to visit and in which order.

Thanks.