If the account has not been used, you can change the currency. Consider the following:
Remove the record from any analysis records where it appears.
Change the P&L Year End code to match the new currency where appropriate.
Redundant analysis codes may need to be flagged as Inactive.
If the account has been used, set up a new account with the required currency instead. Consider the following:
Transactions may need to be reversed from the account and then re-posted to the new account.
The record to be changed will need to be removed from any analysis records in which it appears and these set as Inactive if necessary.
The unwanted record should be flagged as Inactive to prevent accidental use.