Changing Boolean Solver in 2.78? How do I change the Boolean Solver (bmesh/carve) in blender 2.78?

Im using the difference boolean and the result is strange. i want to try the other solver, but I cannot figure out how to change it? Ive seen other people with the option to change it right next to the operation: box, but I dont have that.

What can I do to change the solver?
Check that you are really in version 2.78 - the option should be directly under...