Disabling rigidbody constraints in code - Freeze Position, Rotation etc

I'm trying to disable a rigidbody contraint to allow movement in the Y axis using javascript. I found the page showing how to do it in the script help files, but when I tried a very minor variation of it, it doesn't work, and I get an error. Here's my line of code:
transform.rigidbody.constraints = RigidbodyConstraints.FreezePositionY = false;
I also tried it like this:
transform.rigidbody.constraints = RigidbodyConstraints.FreezePosition = false;
and this:
transform.rigidbody.RigidbodyConstraints.FreezePosition = false;
None of those work, so simple question - How do I turn off the position freezing in code?

rigidbody.constraints = RigidbodyConstraints.FreezeRotationX | RigidbodyConstraints.FreezeRotationY;