iZakaroN's SaveEditor (or from
Kiya's site, with description) does not edit your level directly, but you can edit your experience points to give yourself enough to reach a desired level. Once you reload the game, you need to defeat an opponent or complete a quest to get the game to update your experience and trigger the level update.
The number of experience required to reach a given level is given by the formula below.
E = 1000*(level^3 - level)/3
For example, if you want to be at level 25, you would need to edit your experience to be
E = 1000*(25^3 - 25)/3 = 5,200,000
