Is it necessary to change eye glasses yearly?

No. If their vision is not adequate for their needs, a new prescription may help.
Rarely, . Prescriptions rarely change every year. If changes are significant, see your family doctor first to check you for diabetes, and blood pressure problems, etc next see an ophthalmologist to evaluate you for eye disease. Hopefully, just age related prescription changes. Many patients prescription for distance, computer, and reading is available over the counter! But ask your eye doctor first :).
Not really. But it is not a bad idea to have your vision checked on a regular basis. Frequency can be determined based on subjective ability to see, associated symptoms like headache and family history. A good eye exam can pick up diseases like diabetes and hypertension. If your prescription changes and your old glasses aren't working then at the very least new lenses may improve things.
No! Not at all! In fact I have many patients who's prescription has not changed in many years and they still use the same pair. If your vision is good and your prescription has not changed, why get new ones? Save your money.