I need to edit an invoice which has the wrong Tax categorie.

I need to edit an invoice which has the wrong Tax categorie.

Hi, 

I'm looking a way to change the "Tax section" of several invoices. During the import from another accounting system, it created a different Tax category on a few invoices. It uses the TVA 0% instead of the TVA 20%. When i click on edit, it doesn't allow me to change it.  

Hope someone can help me.

Kind regards, 
Sidney