When redesigning a website, many Web Design Services webmasters feel that they should take the opportunity to fix the lousy URLs or the possibly-ill-thought website structure that they created earlier. For example, over time, you may have learnt that your site can be more logically organised by putting certain files in a particular directory (folder) instead of others. Or you may want to change the filenames of your web pages so that they better describe their contents.
The temptation to do this kind of structural change when redesigning can be overwhelming, and I too have fallen into such a trap.
However, generally speaking, changing URLs and site structure is a bad idea. When you move URLs, the reputation that your old page has established in the search engines is lost since the links pointing to it from other websites will be not be transferred to the new page unless you take special precautions. If you don't know why links from other websites are important, read my article on How to Improve Your Search Engine Ranking on Google.
All is not lost, however, if you strongly feel you have to move an old page. To minimize issues when moving, you will need to redirect all requests from the old page to the new. It is not enough to add a link on the old page pointing to the new. You need to indicate to the search engine and visitors that your old page has permanently changed location. The best way to do this, if your website is running on an Apache web server, is to create a .htaccess file in the directory of the old page, with the following contents:
Redirect permanent /old-folder-name/oldfilename.html http://www.example.com/new-folder-name/newfile.html
Replace the file, folder and domain names with the appropriate ones for your site.
Note that the .htaccess file must be an ASCII text file, not a wordprocessor file. Furthermore, your web host must have enabled processing of .htaccess files on your account. If your website is running on an Apache server on a commercial web host, chances are that it is already enabled. If you are not sure, ask your web host's support department or read their documentation.
An alternative to moving the file itself is to do what I did when I redesigned thesitewizard.com some years back. When I first started this site, I dumped all the articles into a single folder. I belatedly realised that this was a bad idea since, as the site grew, the folder became unmanageable. When I redesigned, I organized all new articles into separate folders sorted according to the general topic. Instead of moving the old articles into these new folders, I merely linked to them from the new category index pages.