Note: You can change your base currency only if your organization is in the Global edition.
To change the base currency, you will have to verify the following:
1. Delete all the records created in Zoho Books.
Access each of the modules under which the transactions have been recorded and delete them manually. Make sure you take a backup of the data in your organization before deleting it.
2. Delete all the custom accounts created from your Chart of Accounts.
To delete the custom accounts,
3. Ensure to delete the Opening Balances in the organization.
You can go to the Opening Balance screen from Settings and delete the opening balance from there.
Once the above conditions are verified, you can follow the steps provided below to change the base currency.
If you have removed all the data listed there and yet the base currency remains unchanged, check if:
Books
Online accounting software
for small businesses.