In Zoho Invoice, you will be able to change the base currency only if there are no transactions recorded. If there happens to be any transactions, you would need to delete them before you go on to change the base currency. To see the categories under which you have recorded transactions, click the change base currency link on the "currency settings" page.

Steps to change the currency:

• Sign in to Zoho Invoice.
• Go to the Settings tab
• Click the "Currencies" sub-link under "Currency & Tax Settings".
• If there are no transactions recorded in your base currency, you will see a Change base currency link adjacent to your base currency's name
• On clicking the link, you'll be shown a list of currencies from which you get to pick the new base currency for your account
• Once done, click the Save button