You can change the invoice currency without having to go into an individual record to update the financial details.
Edit your invoice
Navigate to Accounts > Invoices > click the pencil to edit icon on your chosen invoice.
In the settings panel of your invoice, you have the option of changing the invoice currency. In doing so, it will ask you what the current exchange rate is and provide a link to check the current exchange rates.
Once this information has been added, either in the settings panel or in the artwork details on the invoice, it will then let you know what the new price will be.
If everything looks correct, simply click Done and the financial details will update automatically.
After you generate the invoice, this information will also transfer to the Sale Details section of the artwork record's Financial tab.