I have made invoices in USD, now the client want them in Euro, Is there simple way to convert the invoice to Euro without changing each item ?
Thanks
No
You need to change the customer to Euros as well as the invoices. But you cannot change or delete prior invoices or you will destroy the accuracy of your accounting records.
So, if the customer wants you to change unpaid invoices, issue credit notes for their full value. Then create a new customer denominated in Euros. Then issue replacement invoices to the new customer. The old customer can then be made inactive.