Depending on where You do it you will need to fill the form and some photocopy of your passport, if there is a drive through and you have already proof of residence in your passport you need only your passport.
I did this last year for my daughter (note: this was a different time!) the two schools worked together and got the dates right because I had to move from north to the south of the country too. What nobody told me is that this is not a swap but a whole new application for extension so you need to meet all requirements like proof of residence, money and so on; if you had a multiple entry permit it will be cancelled.
Just be aware of this! and as stated above make sure the new school has all the paperwork done!
thanks for the kind replay and mention clearly all requirements once again!
One question I still have though, could You be so kind please?
In this post the person is already in Thailand and has to leave to get Visa and come back, at the moment the only country one can go to is the home country, isn’t it?