No 1: You don't

No 2: No.

My X-wife would find 'Yes' or 'No' answers unacceptable, my reponse above would drive her crazy. Getting her to give a yes or no answer was like attempting to herd a dozen cats.

Nick

Most Vandas are grown hanging from something because the roots get big and long and like to be free air. If you are trying to keep it potted for display reasons you could just sit the whole thing pot and all into a larger pot, a much large pot.

I don't think you should ever cut off healthy roots. I might not kill the plant but it certainly wont help it.