Android 5.0 update is not always 405MB. It will depends on what device you have and if it will have any extra bloatware added to the stock.
And LG L70 Dual hasn't been confirmed it will get android 5.0
It will overwrite your current Android 4.4 OS to Lollipop. It uses internal memory but it shouldn't take up that much extra space.
What device are you updating on?
Android 5.0 update is not always 405MB. It will depends on what device you have and if it will have any extra bloatware added to the stock.
And LG L70 Dual hasn't been confirmed it will get android 5.0