mobile

My unrooted HTC Desire 816 has just received a rather prominent message sayind "System Update Available. Tap to download the system update." I would like to know what sort of system update it is--is it Lollipop (I read somewhere that this phone wouldn't get Lollipop, and to be honest I was relieved)? Is it an HTC update? How do I know whether I want it? I've heard so many unsatisfactory reports about Lollipop that I have no wish to have it. I've also read some complaints on Play Store about some kind of HTC update. Is there a way to find out what the update is, and, more important, is there a way to refuse it? I just wish I knew more about it and whether I wanted it or not. Right now, there's a big banner across my phone's home screen that gets in the way of my accessing some things not just on the home screen but in play store and other places as well. I've included a link to a screenshot of the top part of my phone's home screen, showing the update announcement that I can't get rid of:

I'm pretty much a newbie with this phone, and I don't want to root it, nor do I want some possibly problematic update to screw it up. It's currently on KitKat 4.4.2, and I'm quite content with that for now. Does anyone know more about what this update is and how I can get rid of the announcement? Thanks in advance for your help.