Here are the steps to clear the system cache:
Wipe cache partition:
With the phone powered off, press and hold the Volume Down button and the Power button at the same time until the device starts to turn on, let go of buttons.
Press the Volume Down button to highlight "Recovery mode"
Press the Power button to restart into Recovery mode.
You'll see an image of an Android robot with a red exclamation mark.
Holding the Power button, tap Volume Up once and then release the Power button.
Use the volume buttons to scroll to "wipe cache partition" and press the Power button to select it.
Select Ok or Yes to continue.
When finished, "Reboot system now" will be highlighted, press the Power button to select it