Dreamweaver has Library Items. You insert a Library item into your pages. When you change your Library item, all the pages which contain that Library item are updated. You then upload all changed pages to the server.
A much better way though is to use Server Side Includes. Much the same as Library items but there's only ever one file to update and upload.
It's funny how 2 people can read a question and get 2 completely different meanings.
Guidance on when to use DW Templates, Library Items and SSIs -