Your Garmin Edge 530 will estimate your FTP as it collects data from rides that you do. Unless you've told it not to, then it'll let you know when it thinks you have increased your FTP level at the end of a ride that you rode hard enough to meet whatever qualifications it looks at.
There is also Garmin's version of an FTP test that you can do. Look in the Training section of the menu and dig down. And there are other versions of the FTP test you can do too to see if you get about the same number. But I wouldn't quibble over the numbers any of them come up with. I'm sure it's close enough to let you base your zones and other stuff you do.