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If you mean can you change a web page from any computer which has DW installed and an internet connection the answer is yes. (And the way that you do it is outlined in the link given above.)
If you mean can you log in from a web interface to change content (like a CMS or Webmasterworld), then the answer is no.
To put it simply, with DW you connect to your site via ftp, open the page you want to change in the programme, save the changes and then "synchronise" it (which means making the copy on the server the same as the one on your computer). You can also make any changes to a site offline if you have a up-to-date local copy, then connect to the server and ask it to synchronise the site, whereupon it will upload any files which have had changes made to them.