How do I update the authentication details/login credentials?

To change the authentication details that you entered when you first set up the NetSuite integration, you need to remove the integration and set it up again using the new details. 

Transactions that have already been exported to NetSuite, as well as any tags added to them, won’t be lost or changed. However, make sure that you set the integration up with the same subsidiary and bank accounts, and import the same custom fields, if you want it to work seamlessly with the same configuration.