How to automatically increase the field "number" in CMS?

I created a help center some time ago, and i want the field number can increment automatically instead of manual, because of an issue when the list of items are sorted by upgraded or created. Take a look at the page:

the item number 7 is not in the right place. how can i fix that?

here is the read only link (go to “Preguntas Frecuentes” page):

Thank for the help