If you're able to close the lid with the mounting bracket on, we suggest you do so.
The adhesive is non-permanent, but pretty strong so you might not be able to take it away with only your fingers.
If you want to remove it, we suggest you use a thin object (like plackers dental floss, a guitar pick, a thin credit card,) and slide it between the magnet and the screen. Gently bend the object backwards so that the magnet detaches.
If you want to use the same mounting bracket to re-position it, read more here.