Documentation > Currency
To change the default currency (or add a new currency) go to Settings > Currency
To change the decimal and thousands separator ( e.g. from 2,310.54 to 2.310,54 ) go to Settings > Advanced and change currency_decimal_separator from . to , and change currency_thousand_separator from , to .
If you need 3 decimal places in the invoice/quote/job tax percents (rather than the default of two) please follow this FAQ article: http://ultimateclientmanager.com/support/faq-knowledge-base/faq-item/112/change-the-number-of-decimal-places-on-taxescurrency/