I want to write letter about my designation change

I want to write letter about my designation change. I joined in this company as a rigging foreman but since beginning I am caring supervisor job & responsibility and wright now my supervisor (who is in-Charge of my Team) on vacation and I am the replacement of him, and I have more than 5 years’ experience in same position also same division. I want to change my designation to Supervisor. So I need your help me to write that letter by the professional way

Thanks''''