Sometimes professional firms will have offered their clients the use of their office premises as a registered office. This is a historic process which is increasingly rejected by Companies House. 

It is important to note that Companies House have removed the 'Care of' field which used to be in place. They are unlikely to accept addresses which refer to 'Care of' in an address, so best practice is to provide the full postal address on its own. 

If you are happy that they just use your full postal address with no reference to your firm, see How do I change the registered office address?