Short question long answer...
If you're indoors with adequate light: move the light up.
Without adequate light: move the light down.
Adequate light but can't move it up: do some bending-- pinch the stem that too tall and roll it in between your fingers for 10 seconds. Bend the stem so its laying horizontally. It only takes a few hours for the branch to turn into a hook shape and straighten out. The plant will heal.
Outdoors: just let it grow or top it.
You can top indoors too, but don't top during flower or preflower and if it's an auto, don't top beyond thirst week.