Upgrading to Joomla 3.1
Please log in to your Joomla 2.5 administration and click on Components -> Joomla! Update. Now click on Options on the top right and select Short Term Support for Update Server. Just click on Install the Update.
Upgrade the theme
To update the theme you've to download the latest Joomla 3.1 theme from our download directory and replace the theme folder of your current 2.5 theme /templates/yoo_templatename with the new one.
Tip: If you have already done a lot of modifications to your the theme, you can also just replace the warp folder with the 3.1 theme warp folder.
Upgrade the extensions
If you have Widgetkit or ZOO installed just re-install the new version for Joomla 3.1 in the Joomla extension manager.