The next time WordPress releases a new version, you will probably want to upgrade to that version. To do that, log in and use the Subversion “switch” command (sw) to switch to a new version (assuming the new version is 2.7):

cd yourapp
svn sw http://svn.automattic.com/wordpress/tags/2.7/ .

Doing so will overwrite any changed WordPress-provided files, while leaving any custom or privately owned files, plugins, and themes alone. In other words, it should be safe (but make a backup, just in case).

Run the usual wp-admin/upgrade.php and you’re done.