Yes you can, so long as you have the required funds in the bank. No requirement to seed the money for the change to Non-Immigrant O. TM 87 form to be completed, bank documents (bank letter, certified copy of bank statement, copy of passbook, balance in all 3 matching), map of where you’re living, then another photocopied set of the same documents. THB 2,000 for the change of visa exempt to Non-Imm O.