i Like to have the mandatory fields of my Information Panel first. Here is according to me the easiest way to change the order.
Open you Library and go Library Settings:
Then Click on Document Information Panel settings and "Create a new custom Template"
This will open InfoPath and after you click finish on InfoPath it will open your Panel...
Move around and do what you want to do and then save(to local machine) it and publish it.
and click publish on the next window and then close.