how i change 'boyfriend' in siri iPhone 4S

All you need to do is tell Siri! So just say ___ is my boyfriend and Siri should now call that person when you say call boyfriend.

Edit: You actually may also need to remove your old boyfriend. Open the contacts app and navigate to your contact information. Edit your contact card and one of the sections should be a list of related people. So for example it says:

mother    ____

father      ____

boyfriend ____

Just remove the entry for boyfriend and then tell siri who your boyfriend is.