I am in the process of renewing my British passport in Thailand. There will be a new passport number. Phone contract (SIM), bank account, driving licences, marriage certificate all have the previous passport number. What do I have to do to update these? Does it need an embassy certified copy of the passport, translated, legalised at the MFA? Hope not!

Don't forget immigration, assuming you're on an extension of stay. They may want TM30 and updated financial information. Bank and phone easy, just go into the office with both old and new passports. Licenses, I never bother until my next renewal, again, take old and new passports. Marriage certificate, no idea, didn't see mine from the day I was married till the day I got divorced. None of these should require any translation or certified copies, other than your own signature.

Most people don't bother about changing the driving licence. The bank definitely and same for your mobile phone service provider.

Most people do visit Immigration to have their stamps transferred. Like @Upnotover I didn't bother as I thought I would wait until my next extension. I got 'caught out' because I had a trip to Vietnam and got pulled up by Immigration- who did the transfer of stamps at Suvarnabhumi airport. The good news was no 500 Baht charge like I get at my local I/O..