Step 1: Go to the invoice with instalment payment

Go to the member's profile -> Billing -> click on the invoice with instalment payments

Step 2: Change the payment method for all upcoming payments

Click on the three small dots next to the payment from which you want to change the payment method -> click on change payment method

Choose the new payment method. If you want to apply this change to the following payments on this invoice check Apply to future instalments of this invoice.