To change the order of the fields of the registration form shown below, please follow the steps below.

STEP 1: Go to Admin Control Panel  -> Setup 

STEP 2: Then Click on the link says "I want to set up my sign-up page to register new users"

STEP 3:  Now click on the Form Fields.

4: Click your mouse and hold and then drag the field to the new location and release your mouse once you have it in the new location that you want.