If you are using Joomla 1.7 and planning to upgrade it to Joomla 2.5 via Joomla automated upgrade, then you may follow the instructions below :
Login to the backend of your Joomla 1.7 and go to the Extension Manager
You will see a Update Tab in this page.
At the top right of this page you will see a button called “Purge Cache” to see the message for upgrade.
All the updates available for your joomla website will show up. Be sure that you will upgrade the Joomla Core 1.7 to Joomla 2.5 first
Now click on the check box infront of Joomla 2.5.x and press the upgrade button at the top right of the page.
Wait for a moment till it upgrades automatically : You may now end up with two outputs, either without errors if you are lucky enough or may have few errors, dont get shocked, the errors can be fixed.
In Both Cases (!) go to a new Tab you see under the same Extension Manager called “Database” (yes…even if the system states ‘successful!’). Now you will either see a message that all is ok or a warning with a list of errors or missing DB entries.
These we correct now by clicking the “FIX” button located in the Database Tab Top right corner!