You can change the currency symbol by using the following code:
/**
* Change a currency symbol
*/
add_filter('woocommerce_currency_symbol', 'change_existing_currency_symbol', 10, 2);
function change_existing_currency_symbol( $currency_symbol, $currency ) {
switch( $currency ) {
case 'AUD': $currency_symbol = 'AUD$'; break;
}
return $currency_symbol;
}