Before you perform an update, make sure you have a backup of the current Pagekit installation and your database. That way you can always recover previous states of your installation in case something goes wrong.
The recommended way of updating Pagekit is through its admin panel. Open System > Update and click the Update button. To make sure that the update was successful, just open System > Info. If everything went smoothly, you should see the new version number under the System tab.
Note It is possible to update Pagekit manually, although it's not recommended. To do so, download the latest release from http://pagekit.com and extract the archive. Then upload the folder to your webserver and overwrite the existing files in the Pagekit folder. A database update (if present) is triggered after logging in to the admin panel.