Breaking through from one realm to another, was simple.
All one had to do was to utilize energy, either theirs or energy gotten from an external energy core to strengthen their bodies to be able to hold the amount of energy required for the next realm of existence.
Once they reached the limit of what they could absorb, they were to stop absorbing and begin circulating the energy currently in their bodies.
If they were not at their maximum capacity, then they could absorb more, but if they were, it was advisable to stop to prevent the situation of one imploding due to excess energy.
After circulating their energy to the limit, they were to utilize said energy to push through and forcefully break through the upper limit of their energy reserves, the upper limit of what their bodies could hold, and elevate said limit to a higher level.
Your gift is the motivation for my creation. Give me more motivation!
Creation is hard, cheer me up!