You can change your name by Deed Poll by visiting
http://www.deedpollservice.com. At the time of posting this reply the cost of an adult Deed Poll is �25.
As for using the title Mrs instead of Miss, you can do that without going through any procedure at all. The use of titles such as Mrs, Miss, Ms and Mr are purely cultural in the UK and therefore you can use whichever one you like.
To change your title you should add something like "Following my change of name by Deed Poll i have also decided to change my title from Miss to Mrs." to the covering letter that you send along with your Deed Poll to the organisations that you are informing.