If you have been driven crazy by the offers of upgrades to macOS High Sierra, here is my holiday gift to you: hide the upgrade banner, which should turn off the reminders:
- Open up the Mac App store.
- Click on “Updates.”
- Right-click or Control-click (hold down the “Control” key while clicking) on the High Sierra banner image, and select “Hide Update.”
If you eventually decide that you want to install High Sierra, just go to the App Store Featured page and look for it on the right.