The way professions work is that at level 5, you are able to pick between two, and the one that you select determines which two you will be offered to choose between at level 10. So while there are four possible options for each profession at level 10, you will only ever be selecting between two at once, because your choice at level 5 means the other two won't be presented to you.
For example, in combat, at level 5 you pick between Fighter or Scout. If you select Fighter, at level 10 you will get to pick between Brute or Defender, while if you select Scout, at level 10 you will see options for Acrobat or Desperado.
When you switch professions, you should be presented with the option to re-select both your level 5 and 10 professions.