Downgrade to Medishield

I wish to downgrade from a private Shield to Medishield. I have a lot of trouble with this request.

My enquiry to the insurance company was not properly answered. I was given a form to cancel my private Shield, but there was no mention about the downgrade to Medishield. I have to ask again for them to answer this question.

I search the CPF website. They said that the member can downgrade from a private Shield to Medishield at any time, but did not indicate how this can be done. I have to write to them for instructions - as I am not able to find the instructions in the website.

I prefer to be self-insured and pay out-of-pocket for my hospital charges. However, if the medical charges are very expensive, I can opt to be treated in a subsidised ward.
http://www.tankinlian.com/articles/health.html