How do electrons from one orbit get to another orbit?

They emit or absorb light. The electron in one orbit has a specific amount of energy. The electron needs to have a different energy in order to exist in a different orbit. When light shines on the atom, if the electron can absorb just the right amount of energy from the light, then it can jump to a different orbit. Let me make up an example. Let us pretend that an atom has red light shone upon it and it absorbs this and an electron jumps from 1S to 2S. No matter how much red light you shine, the electron will never jump further! Brighter light will allow more atoms to have electrons jump from 1S to 2S, yet none go higher. But if I shine, say, green light on the element, then electrons will jump from 1S to 2P. How odd! If I make the green light dimmer, fewer atoms have an electron jump from 1S to 2P. If I make the green light brighter, more atoms have an electron jump from 1S to 2P, but only that transition. Further, it may be possible that after shining bright red light on the atoms, I find that yellow light makes the 2S electrons jump to 2P. Hmmm very suspicious!