Deed of Release Question

My garden has a lease. My Property is Freehold. In 2012 I paid the leaseholder a redemption for the rent charge. For this I received a Deed of Release. How do I go about getting the garden title changed so it changes to a Freehold title?

Maurice - if it's a registered rentcharge, so it has it's own title, then you can apply using form AP1 plus the evidence of the release.
If it's noted, so on your own title, then it would be a form CN1 plus the supporting evidence 
£40 fee payable for either application, post only, and paid by cheque/postal order to HM Land Registry

Thank you so very much Adam. You have been so helpful! :-)