Changing templates with Dreamweaver is not too difficult although just editing your existing template is easier. The main point to keep in mind is to make sure that your "editable regions" are kept consistant. If you have an "editable region" in your original template make sure you have it in the new template, so when you apply the new template Dreamweaver knows where to put the data within the region. If you do have a lot of pages, applying a different template to each page is a bit tedious, whereas if you edit your existing template, Dreamweaver will find each page that uses the template and update it for you. You still have to upload each changed page when you are done either way.