Hii Ranjit,
Please see the clause of conitunuance of business by remaining partners in case of dissolution in original deed. What your original partnership deed said about the continuance of business in case of outgoing partner. And as far as the registration of deed, there is no compulsory provisions regarding registration of the deed but it will be good for the firm to get register it. As the firm can sue only after registering itself with the registrar of firms & societies.
And if there is a provision in your original deed for continuance of business than you have make a ded of dissolution & in the same deed you can enter new partners.
And if there is no provision regarding continuance of business than make changes in the clause by making a subsequent deed with original partners.
I hope this will be help for you.
Regards,
Amit