If you mean “change” as in, handover a MasterCard credit card at a counter and receive a Visa credit card across the counter, it’s not possible to change MC for V credit card.
You need to cancel your MC and apply for a new Visa credit card. Not all banks offer both V and MC, so you might even need to change your bank.
One important point to note: Part of the 16 digit credit card # identifies the card network i.e. whether V or MC. So, your “change” of credit card would entail a change in credit card #. You’d need to update your card on file at all merchants.