vCenter 2.5 Update 4 is available download and official released by VMware. You can read through the information from here

I had just done my vCenter upgrade today from 2.5 Update 3 to update 4. I notice some graphic interfaces changes compare to the previous version. Databases upgrade is required during the installation process. I will suggest to backup the databases related to virtual center before you perform any upgrade to your production environment. If anything goes wrong, you should able to restore your databases immediately. The Databases upgrade is supported with both Microsoft SQL and Oracle.

This GUI interface allow you to retain all the previous data of your virtual center. If you wish to refresh your database, you can choose Drop or Discard from the option above.

Upgrade in progress

Upgrade completed and you should able to see the summarize of the upgrade option.