The update process is very simple, and complete instructions are available here. Note that there are easier and better ways of updating than copying the files with FTP.
2.5 End of Life Update
As previously noted, the 2.5 series will reach end of life at the end of 2014, which will mark the end of support for this series. At this time, we project that 2.5.27 will be the last scheduled maintenance release, due in approximately six to eight weeks, the typical timeframe between Joomla! releases.
Download
- New Installations: Click here to download Joomla 2.5.26 (Full package) »
- Update Package: Click here to download Joomla 2.5.26 (Update packages) »
Full announcement: http://www.joomla.org/announcements/rel ... eased.html
Discuss the release: http://forum.joomla.org/viewtopic.php?f=9&t=860453