Do you have any experience with updating the joomla core from 2.5.1 to 2.5.3? I would like to update our master site: joomla and jms. Can you give me the steps to follow please? I wonder if i have to uninstall some things in joomla or jms first. Do i have to update first joomla and after this jms? At least checking updates for patches?

The update of Joomla with Joomla 2.5 is easier than in Joomla 1.6 or 1.7.

In joomla 2.5, once you have updated your master, you can go in the "extension manager" / databases menu an click on fix.

You have to repeat the operation in each slave sites.

This procedure can also be used when upgrading from Joomla 1.7 to Joomla 2.5

I see there is a warning now in master. Database version is 1.7.3, cms version is 2.5.1. Can i first upgrade to 2.5.3 and after this do the fix from database. So it will be a fix from 1.7.3 structure to 2.5.3. Is this operation riskfull or is there nothing to fear?
Do i have to repeat this database fix in each slave everytime i update joomla in the master site? I thought it was the main goal of Jms, Edwin, only having to update one joomla version for all sites?

I personnally already upgrade Joomla 1.7.x to Joomla 2.5.x with the upgrade of the master and after use the "extension manager" / database / fix procedure on each slave sites and that had worked.

As any upgrade, it is recommended to perform a backup before proceeding to the upgrade.