like "rogerkiu" said; to remove the plastic half glued to the windshield, it will become damaged beyond use.
The two halfs.
Once you half the halfs separated you will notice that the one that attaches to the windshield is basically plastic with glue on one side (the glue is of a like solid silicone consistency)
The other half will have the electronics and metal clip attached to back of it.
When installing make sure the two plastic parts clip back together.
The metal clip will then hold clipped plastic assembly to the window mounted trim.
Make sure everything is aligned as you are installing things.