I will have to go to the immigration soon in Bangkok to extend my tourist visa. I now have a new passport, so was wondering if I take both passports to the immigration, will they simply transfer the current TV stamp to my new passport and add the extension, or is there another process I need to do first before I get the extension?

Thanks for any help

You should have done the transfer when you obtained the new passport so first stop I suspect will the the office for new/lost passports where they will transfer the permitted to stay stamp (full set of copies required) and then another stop for the extension.