As usual each time a major new version of Piwigo is released (version 2.5 this time) many Piwigo.com users ask how to upgrade. It’s nice to see how motivated you are! But you will have to be patient. As said on blog post Piwigo 2.4 and upgrade on Piwigo.com :
On Piwigo.com, you don’t manage updates, so it’s useless to try by yourself. The update to Piwigo 2.4 will be applied automatically without any action from you.
Version 2.5 is a much smaller step than version 2.4 was. It means that plugins and themes are simpler to adapt and that upgrades will occur sooner. I hope first photo galleries will be upgraded in less than 2 weeks.
Once your gallery is upgraded to version 2.5, you are notified by email with a summary of changes. The main advice to have your Piwigo upgraded to 2.5 as soon as possible: deactivate plugins you don’t really use.