I want to change number of ring times or duration system wide before it goes to voicemail. I am wondering how to do that.
What version of UCM are you running?
In v6.x, go to System --> Service Parameters, select a Server, select the Cisco CallManager service. Search for "Forward No Answer Timer", and you can change the time in seconds to what you desire. I've found that a ring equates to about 4 seconds. After you've changed the timer, click Save at the top of the screen.