This is the "security gate" that allows you to install unofficial software. Custom Recovery: Tools like

Contrary to popular belief, Android 5.0 Lollipop introduced – a battery-saving feature. On older hardware, a well-optimized patched Lollipop build runs smoother than KitKat.

via a "patched" download is a classic DIY tech project, but it requires a bit of caution and prep work. Since official over-the-air updates for these versions ended years ago, you are likely looking at using a Custom ROM