To change the layer order, expand the
Draw Order node in the Tree view, click the slot which you want to modify, then drag it up or down. When performing this operation in Setup mode, the change will affect all animations. In Animate mode, the change can be keyed on the timeline in the active animation. Please see this page of the user guide for more information:
Slots - Spine User Guide: Draw order
By the way, we have a topic for questions about the Spine editor (viewforum.php?f=11), so if you have any more questions, I hope you will post them in there.