Magento 2: Add after/before positioning in pre existing xml block/container
<move element="checkout.cart.shipping" destination="cart.summary" before="-"/>
This link helps me.
how to change block ordering in layouts
You can use move tags to move blocks.
<move>
instruction: allows changing element's order and parent.
<move element="logo" destination="login.header" before="-"/>
element: name of the current block/container.
destination: name of the destination block/container where you moving element.
before: name of the block before which you need to move your block.
after: name of the block after which you need to move your block.
Refer this for more information: http://devdocs.magento.com/guides/v2.0/frontend-dev-guide/layouts/xml-instructions.html