Adding

In order to add a new rate you must navigate to the Control Panel ->  VAT. Here you will see a list of existing VAT rates in the system which will typically be 20% and 0%.

To add a new rate you need to click new which opens a blank form and enter both the name and the percentage rate.

After clicking save it will add the new VAT Rate and it'll be usable throughout the system for example on products.

Editing 

To edit a rate you can either double click the row or you can use the right click context menu and 'Edit' to open the edit form. 

Deleting

To delete a rate you simply need to select 'Delete' from the right click context menu. On click the rate will disappear from the form.