How do I de-register VAT

I've recently de-registered for VAT, & want to update freeagent. I see where I can update my VAT registration status to 'Not Registered' - but I was concerned if I changed the status I'd lose my VAT accounting for the past few years, which I do need to keep? And for my accounts to be correct, I would have thought I'd need to enter a VAT end date?

Please could you confirm if it is possible to de-register for VAT and what's the correct way of doing this?

Thanks very much, Ben