Hi Thejas,

The required steps are nicely listed in this doc;

Installing and Upgrading Cisco Unified CME Software

http://www.cisco.com/en/US/products/sw/voicesw/ps4625/products_configuration_guide_chapter09186a00808777e0.html

This thread has a nice note from Paolo!

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1dde8b54/2#selected_message

Why don't you start by upgrading IOS to 12.4(11)XJ4, for CME 4.1. This seems to be a highly rated and stable IOS/CME combination.

12.4(11)XW2 - CME 4.2

12.4(15)T - CME 4.1

12.4(11)XJ - CME 4.1

From this doc;

http://www.cisco.com/en/US/docs/voice_ip_comm/cucme/requirements/guide/33matrix.htm

Hope this helps!

Rob