How to change default payment method.

In entry file of the extension we need to extend the OrderWizardModulePaymentMethodSelector module.

CODE :

define(
    'Extension'
    , [
        'OrderWizard.Module.PaymentMethod.Selector', 'Utils'
    ]
    , function (
        OrderWizardModulePaymentMethodSelector, Utils
    ) {
        'use strict';
        return {
            mountToApp: function mountToApp(container) {
                var layout = container.getComponent('Layout');
                _.extend(OrderWizardModulePaymentMethodSelector.prototype, {
                    getContext: _.wrap(OrderWizardModulePaymentMethodSelector.prototype.getContext, function (fn) {
                        var originalRet = fn.apply(this, _.toArray(arguments).slice(1));
                        return originalRet;
                    }),
                    //default_payment_method_section
                    render: function () {
                        if (this.wizard.hidePayment()) {
                            this.$el.empty();
                            this.trigger('change_label_continue');
                            return;
                        }
                        _.each(this.modules, function (module) {
                            module.isActive = module.instance.isActive();
                        });
                        this.wizard.options.profile.attributes.paymentterms = 'creditcard';
                        if (!this.selectedModule) {
                            var selected_payment = this.model.get('paymentmethods').findWhere({ primary: true });
                            var selected_type;
                            if (selected_payment) {
                                selected_type = this.isOthersModule(selected_payment.get('type'))
                                    ? 'others'
                                    : selected_payment.get('type');
                            }
                            else if (this.wizard.options.profile.get('paymentterms')) {
                                selected_type = 'others';
                            }
                            this.setModuleByType(selected_type, true);
                        } else if (this.selectedModule.type === 'paypal' && !this.model.get('isPaypalComplete')) {
                            this.trigger('change_label_continue', Utils.translate('Continue to Paypal'));
                        } else {
                            this.trigger('change_label_continue');
                        }
                        if (this.isOthersModule(this.selectedModule.type)) {
                            var other_module = _.findWhere(this.modules, { type: 'others' });
                            other_module.isSelected = true;
                            this.selectedModule = other_module;
                            this._render();
                            this.renderModule(other_module);
                        } else {
                            this._render();
                            var selected_module = _.findWhere(this.modules, { isSelected: true });
                            this.renderModule(selected_module);
                        } if (
                            Utils.getParameterByName(window.location.href, 'externalPayment') === 'FAIL' &&
                            this.showExternalPaymentErrorMessage
                        ) {
                            this.showExternalPaymentErrorMessage = false;
                            this.manageError(this.externalPaymentErrorMessage);
                        }
                    },
                });
            }
        };
    });

Output : 

The default payment method changes to Credit card / Debit card from Invoice.