If you believe your taxable turnover in the next 12 months will not exceed the VAT deregistration threshold (£83,000 at the time of writing) then you can apply to be deregistered for VAT.
You will need to satisfy HMRC that you have good grounds to believe your turnover will be lower, for example:
HMRC can refuse your application if they are unsure your taxable turnover will be lower.
Some other points:
HMRC will not allow you to cancel your registration if you are only going to be under the deregistration threshold by suspending your sales for 30 days or more.
Once you are deregistered for VAT then you need to keep checking you don’t go over the VAT threshold again. Your turnover calculation will start from the date you de-registered.
You can apply online through your HMRC login.
Conclusion
If you know that a change in your business means you won’t exceed the VAT deregistration threshold then you can apply for voluntary deregistration.