Before my son enrolls at school in Thailand,he stayed with DTV visa under my guardian.But now he is enrolled in school and they told that he can not stay with DTV .He need to change ED visa back .And told us that ED visa cannot be swap in Thailand.At first ,we have to cancel his DTV visa and leave the country and come back with TR visa.And then they can change the Ed visa .But i don't know DTV can be cancelled or not and what is needed to do.