The link here is the best way to update a WordPress blog.
Quick summery for myself so I do not have to look at the link anymore.
$ cd blog
$ svn sw http://svn.automattic.com/wordpress/tags/2.3.3/
Find new tags here http://svn.automattic.com/wordpress/tags
Again short post mainly get this out and bookmark it for myself, if you want to read the article follow the link above .