As opposed to deactivating constraints, where the constraint is still present but has no effect, you can also remove constraints permanently from objects.
When you remove a constraint, the object that was constrained does not return to its "pre-constrained" state; however, if you undo the creation of the constraint (press Ctrl+Z), the object returns to its pre-constrained state.
In a viewport with the constraint links visible (see Viewing Constraints and Their Information) between the constrained and constraining objects, click the link and press Delete.
Select one or more constrained objects and choose Constrain 
Remove Constraint. If the object is constrained to more than one object, you are prompted to pick the object from which you want to remove
the constraint.
In the explorer, go to the constrained object's properties (see Finding Constraint Elements in the Explorer), select a particular constraint, and press Delete.
To remove all constraints from an object
Select one or more constrained objects and do one of the following:
Choose Animation Remove Animation from Objects Constraints from the Animation panel.
In the explorer, go to the constrained object's Constraint properties (see Finding Constraint Elements in the Explorer).
Right-click the Constraints folder and choose Delete to remove all constraints in that folder.
