To sort sections of a module, first click on the Sort action link on the menu bar of the Author view.
You will be taken to the Sort Modules View.
Click on Sort Sections as in the below screen shot. Then choose the module you want to sort the sections of. In the New Sequence box, use the up and down arrows to move sections as desired.
When you are finished sorting your sections, click on Author or View and you will see the new order.