A) Copy the old pages to new pages with a better name, and change all the links on your site (and
others) to point to the new page. Then wait until the search engines pick up the new pages, and
either delete the old pages, or replace them with pages containing only links to the new page. It
is critical when using this method that you do not attempt to keep links to both the old page *and*
the new page. Having links to both on your site will look like "duplicate content" spamming to
the search engines. So it is important that you "advertise" only the new page address by linking
to it on your site; links on other web sites to the old page will be given some latitude. This
method is simpler, but the new pages must then build their own page rank - some of which will
come from being linked-to by the old pages.
B) Rename the old pages to new names, and use a server permanently-moved (code 301) external
redirect to "forward" the old URL to the new URL. Change the links on your site to point directly
to the new pages. You can take the redirects down after the search engines pick up the change by
following the redirect, or you can leave the redirects in forever. Google follows the 301 redirect
and (for me anyway) gives the new page the PR of the old one, and drops the old page.
How you implement the redirects depends on what server your site is hosted on. It's simple enough
with Apache (with which I am familiar) and I've seen several posts here on how to do it for M$
servers; Use site search here on wmw to research "redirect", "redirect", and
If there are links on external sites pointing to pages which you have renamed, it's a good idea to
leave the redirection to the new pages intact until all or most of those have been updated. Some
here say that once a URL exists, then it should never go away. But at some point, the trade-off
between supporting the old URLs and keeping my sanity doing site maintenance compels me to kill
off old pages after a decent interval.
The critical consideration here is whether the Page Rank that each of these pages has comes mostly
from your on-site links or from external sites deep-linking into them. If the pages' PR is mostly
externally-derived, I wouldn't even try method A. If it's internally-derived, and you change both
the internal links and the page names at the same time, then the new page rank will be the same as
the old because the calculation will be the same as for the old pages, so either method will
probably be fine.
Hope this helps,