If your job and base lvl is over 30 (you have to be 2nd job) you can perform a limit break (Ragnarok Online Player know this as "Rebirth").
You'll return to a Novice (lvl 1) again, but you'll get more status points for the beginning and your job level limit will increase by 10! So you can level up to job lvl 99 !
The amount of extra status points you'll get depends on your base lvl (high level = more status points).
It's really usefull, 'cos with limit break you can max all your stats/skills^^
Just do it very often.
You have to go to the job guild you're belonging to and have to talk to the guild master. He'll let you make a limit break.
And you can change your job to an other job then you were before.
example:
you (lvl 63/39 Hunter) -> limit break -> Novice (lvl1/1) -> leveling and jobchange -> Swordman (lvl 39/30) -> knight (lvl 51/30) -> limit break -> novice (lvl 1/1) -> leveling and jobchange -> Dark Knight (40/30) -> limit break -> and so on....