How to update company name, tax number and other details in the invoice?

Changing a specific invoice is possible only if you have not already saved it and only in the same month the payment was made.

To edit your invoice, log in to your dashboard and click on the top right picture of yours and select "Invoices". Find the invoice which you would like to update and click on "Print Invoice" next to it as shown below. This should open up a page with default billing details from your account. You can edit and save this information, provided it was not saved earlier and the payment was made in the same month. If the invoice is already finalized then it will directly download the invoice without allowing you to edit the same. 

To update your default billing details visit your dashboard and click on "Update Details" below your profile card and enter the details as shown below. These values will be used as default details for your future invoices. 

Please note that GST number can be updated only on Indian payments and not on Export invoices. If you wish to display a VAT/Tax number on your Export invoice, you can add the same next to your company name, for example, "TransTech Restaurants LLC (VAT: 987654321)"