First, you should instruct a conveyancing lawyer to deal with this as they should be used to dealing with the Land Registry on such matters. Many, if not most, residential properties in the England and Wales are owned as joint tenants rather than tenants in common. There are substantial inheritance tax advantages to owning it in this way as effectively the joint owners each have a 100% share of the property, so that upon death the survivors still own all the property and there has therefore been no taxable disposition.
More and more owners are receiving tax advice suggesting that joint owners to own a fixed percentage of the property so that they can Will their share upon their death, rather than to leave it to the survivor. To do this it is necessary to sever the joint tenancy. Before embarking on this process please speak to your accountants and Conveyancing lawyers and there may be side issues from both a conveyancing and tax perspective. Severance is a two stage process. First, a notice in the required form is served upon the other joint tenant or joint tenants . The notice will specify the shares that you have respectively agreed to own in the property (or, in the absence of such agreement, that you own it in equal shares). Secondly a Land Registry form is sent to the Land Registry requesting the entry of a Restriction in the B section of the Register of Title. This prohibits a sale from taking place by one party without notice to the others.
If the other joint tenants do not agree you can still sever the joint tenancy but it will be on the basis that you each own an equal share in the property, and the notices will have to be prepared on this basis.