You can change VAT easily. If it is the same all the time, change it from the invoice settings (Settings - Invoice Settings - Invoice row).
From there you can choose or enter your preferred VAT rate. You can also choose whether or not VAT is shown on the invoice row, and whether the prices are with VAT or without VAT:
If you wish, you can also do all this when preparing the invoice and even choose a different VAT for each row of the invoice. To do this, click on the unit price field and select your desired settings:
