For Jira Server, there are two versions of Automation for Jira, the Lite (free) and the Pro (paid). Here is the comparison of the features:
It shows that the Field Value Changed triggers is only in the Pro version.
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events