I'm not able to change it for some reason.
I've been emailing backwards and forwards to Shopify for days about this - I have a non-VAT registered company and am a sole trader in the UK. Nothing I have sent (tax returns, HMRC identity documents etc.) seems to satisfy Shopify who have given me (and everyone else I guess) around 14 days to get this done before they begin refunding customers' payments and stopping my payments. They have already suspended payouts that I believe are legally mine as goods have been sent. This will essentially put me out of business.
DISGRACEFUL. I'm looking at swapping to ShopWired - at least they are in the UK and may offer a better level of customer support. Shopify STINK on this matter.