First of all, with on your home screen, swipe DOWN from the top. You should get your drop down menu, like this:
Tap the settings icon.
From there, tap the STORAGE option from the list:
Next, go down your list and tap the TOGGLE buttons to the "on" position. When they're "off" they are grayed out. If they're "on" then they're orange.
I personally have all of mine turned on. It frees up space on the internal storage plus allows your kindle to run faster.
Please feel free to let me know if you have any questions or concerns!