Start the game on Easy and play until you have gotten past the first Djin. Upgrade at least 2 things to the next level, then start a new game on Normal. When the game begins, switch the difficulty to Easy and then follow the story till the first Djin again. Just after that area you will see that your upgrades from the previous game will appear and all the XP in the levels have been reset (Monsters and Sarcophagi). Repeat as many times as desired and you can have all the available upgrades; and you can save up upgrade points for the later unlocked ones.