Upgrading to 2.6.3 (where is the guide)

The codex page on upgrades is here
http://codex.wordpress.org/Upgrading_WordPress

However the easiest way to upgrade is to install the WordPress Automatic Ugrade plugin.

Download from here:
http://wordpress.org/extend/plugins/wordpress-automatic-upgrade/

unzip and copy the folder into your plugins folder
wp-content/plugins

in the dashboard go to plugins – find it and activate it. Then start it up. It will back up your database and files before it changes anything (unless you tell it not to)