Fields on Web Forms can be reordered easily by:
Editing the List
Selecting the field on the form you wish to move and dragging and dropping it in it’s required location.
Then Saving your changes
Please note: This will not change the order that the field headings are in inside of your contact list just how it will display on the web form.
If you wish to change the order of the field headings / columns in your database, this can be done under CONTACTS by reordering the fields in your Table Settings and Saving the changes.