Without going into much detail scripting just open script.rpy and change all four instances of _XPgoal = 100 to a lower number, like _XPgoal = 50 or even _XPgoal = 1
Do not use TAB for spacing, renpy games hate tab spaces, use spacebar.
If want to level even faster there are four instances of how much exp is needed per level which are P_XPgoal = int((1.15 * P_XPgoal) + 100) where P_XPgoal is for the player, R_XPgoal for Rogue, etc. Every character gains 10 exp for each class and study event.
While you have the file open if you are using a text editor with a line counter, read line 74, maybe its a hint to whats next in the pipeline.