ANSWER:
You have to change into a special mode to edit the TAB order. Click "Edit > TAB Order". In this mode a number is displayed on the operator-controllable image objects. This is the TAB order number.
Please proceed as follows to set a new order of the objects (starting with number 1):

1. Click the image object that is to be the new number 1. Then set the remaining order of numbers by clicking the relevant image objects one after the other.
2. If you want to correct the TAB order and make a different image object number 1, then keep the "Shift" key pressed and click the appropriate image object.
3. Once you have assigned all the numbers, you can exit the TAB order mode with "Esc".

If you don't want to start with number 1, then please proceed as follows:

1. Switch to the TAB order mode (proceed as described above).
2. Define your "Start number" (not equal to 1) by pressing the "Ctrl" key and clicking the image object with the required number.
   Example:
   If you click the field with the number 5, then this is your start number.
3. Release the "Ctrl" key.
4. Define the subsequent order of numbers by clicking the relevant image objects one after the other.
5. Once you have assigned all the numbers, you can exit the TAB order mode with "Esc".