The Job Details screen displays detailed information about the selected job.
You can also see the jobs required as a condition for the selected job, as well as the higher-level jobs that are conditional on the selected job.
You can pay job points to raise the job level.
You can refund your job level by using the material item "Oblivion Orb".
(You can return it to job points and reassign it to another job.)
One level can be regained per Oblivion Orb.
If a qualifying higher job level has been obtained, the lower job cannot be refunded.
(For example, if you do not refund the knight level until it is reduced to 0, you will not be able to refund the job level of the warrior and monk.)
In addition, all job levels can be reset at once by purchasing "Job Level Reset" from the Shop screen.