You mean change the order of fields?
Unfortunately this is not possible, the order is fixed.
However you can add the "seller / customer" as a fixed field so you will not need to add it every time manually.
To do so follow these steps:
1) Go to "Businesses & customers" and create a generic payee (for example call it "..")
2) In the "Actions" screen long press the buttons area at the bottom of the page. Select the "+ button" to add a new button and then "New action+shop, store". Now select the generic payee you created in step 1.
This will add a button to the "Actions" screen. Whenever you press this button it will create a new action with generic "seller/ customer". You can then change this "seller/ customer" to whatever you want.
In order to save time you can also create more buttons like this with popular sellers / customers.