If you had given your Pin to someone and you no longer trust them. If you notice suspicious transactions e.g Someone keeps buying Airtime to their line without your permission.
If someone applies for Mshwari Loans with your phone without consulting you
Procedure on How to Change Your Mpesa Pin.
1.Go to Mpesa
2.Choose My account
3.Choose Change Pin.
4.Put your Old Mpesa pin then press OK
5.Put your New Desired Mpesa Pin
6.Confirm your New Pin in the next step
7.Wait for Confirmation SMS.