I used to be a GM on Ragnarok Online and I can tell you that there are no cheat codes for players. The commands that increase your level or stats are restricted to power users like GMs. This might be wrong though if you are playing on a pirate server where the "cheat" commands have been made available to the players.
One question though - Why cheat if the fun with playing RPG's are the actual leveling and becoming better?
I find this request funny, escpecially on these forums...
Edit: The power user commands usually start with @. Try @level 10
your name.