ummm, yeah, just use a variable to save the level, and then use a con. branch to cherck the level and change if it's above
so...
Common Event: Trigger: Switch [Level Check]; Parallel Process
Control Variable: Variable [XXX: Jay's level] = Character: [Jay]'s level
Conditional Branch: Variable [XXX:Jay's level] >= 20 (20 is the level you want to change graphics at)
Change Hero Graphic [Jay] -> some graphic
Control Switch: [Level Check] = OFF
Branch END
Remember, the switch Level Check should be turned on at some appropriate time.