how to change default qmake path/version in mac os x?

[abdol]

Hi every one,
How can i change the default path of qmake? I already have it in:
/opt/local/lib
to a newly installed:
/usr/local/trolltech/qt-4.7.3/bin
but I want to change it to the newly installed version. (I don't have qt creator installed)
I am using mac os x and new to Qt.
Thanks,
Abdol

*** To add some explanation, I have 2 installations of Qt, the 2nd one is newer and I want to use the 2nd one by default, and when I type: qt -v in terminal see the 2nd path.