how can a system automatically changes the workflow stage when a field is updated

[Yamini]

For Eg: when a user updates on the acknowledgement field the system should automatically changes the workflow stage as completed. is it possible to do in Jira

[Nic Brough -Adaptavist-]

You'll need to find or write a "listener" that can pick up any event where the field might be updated, and issue a workflow change based on it.

Have a look in the marketplace, you might find it easier to work with an Automation or Scripting add-on than start from scratch on your own.