You have a high quality PSU (built by Delta Electronics) which will provide you more than enough power to run your system. You don't need to change it at all.
Take in mind the Power Supply Requirement for your graphic cards (whole system):
450 Watt or greater power supply with 75 Watt 6-pin PCI Express® power connector recommended (550 Watt and two 6-pin connectors for ATI CrossFireX technology in dual mode)
Here you have a review: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=110