How can I stop adverts from "System Update" from showing up on my lockscreen on a Micromax phone?

It's been quite some time since I last used Android, but following the untimely death of my old "roaming" phone while travelling in India, I've just ended up buying myself a Micromax Q338. This runs a Micromax modified version of Android 5.1 Lollipop After uninstalling or disabling a few of the annoying apps it shipped with, I'm still faced with one issue - adverts showing up as notifications on the lock screen, which seem to turn up when / just after connected to the internet. If I touch and hold on them, they show as being from *System Update*, as shown here: Lockscreen / Notification settings (click images for larger variants) As far as I can tell, *System Update* is an official component, and not a third party app. As such, I don't think I can/should uninstall it. I also can't find *System Update* under Settings / Sound & notification / Notification / App notification, so I can't apparently disable them that way. So, how do I stop System Update popping up adverts on the lock screen when there is / has been internet?