Hair all goes weird once I change the mesh I have made this character, and I want to seperate the helmate from the body.
But soon as I delate, seperate, modify the helmate, the hair just all goes wild.
(Half of them would move to different place)

I used the body to make hair directly.

Someone save me please.
It's easy before going into edit mode go to particle system disconnect all hair system by clicking on "disconnect hair"
Edit your mesh and reconnect hair
NOTE: - if you have activated children of hair then first connect the hair and re-activate children 
To re-activate Children: - go to children tab in particle group and click on "none" Then click on 'simle' or 'interpolated' by your choice.  

Hope it's helpful to you.