You shouldn’t promise something you can’t be sure you can deliver—like a raise or a promotion. Focus on what the change is expected to do. If that might open up opportunities for advancement, you may mention that but as "one possible result," nothing more.
Turn the change plan itself into an opportunity by pointing up the negative risks if the change isn’t made. Should you still have doubters, the first payoffs in a business sense as you implement the plan should raise enthusiasm and convince people of the wisdom of the new approach.
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Alter the gripes and groans to cheers and enthusiasm by keeping the gains or benefits of the change in the forefront of all conversations about the change. This is certainly the time to stress the positives and thereby override the understandable uncertainties, fears, and anxieties. For instance, when talking about the need for the change, don’t neglect to point out the consequences of not implementing the change. And use pilot projects or trial runs wherever practicable prior to making the change final. Experimental runs can help to "debug" the change effort before the total change is implemented, and such trial runs will provide concrete evidence that the new approach is realistic and workable.