Leveling up operates in accordance with the amount of Experience Points (XP) accumulated. Each level requires a certain amount of XP (may look like crystals) and one needs to collect the requested amount of XP to level up. They can be earned by completing the tasks or merging the level items which will give the Experience Points as an extra bonus. Note that the Experience Points are mergeable as well and the highest level will reward up to 50 XP!