@SSeven ******
do you already have a Thai bank account? Without one you can't change to a Non-O visa inside Thailand. Be aware that the court process can take months.
If you have a Thai bank account you need to put the required funds in it before you can apply and you must have between 15 and 21 days left on your current stamp to apply, you can get the extension and use that stamp if you wish. Check the exact requirements with your immigration office.
Otherwise you'll need to apply for the 90 day Non-O visa outside Thailand