To update the currency for your annual report go to Settings>Defaults>Basics and select the corresponding Language and Country.  Note that the setting for 'currency' will not be reflected in your annual report.

This is particularly important for Australian users who tend to set their language to 'English (GB)' but would like their annual reports to display '$' for AUD.  By setting the 'Control panel language' to 'English (GB)' the annual report will display the monetary symbol for GBP '£'.  To have your records appear as '$' you need to set the language to 'English (US)'.

It is not possible to update the currency symbol on annual reports for years that have passed.  Any changes will only be reflected on upcoming annual reports and cannot be applied retroactively.