Updating High Sierra installation is not progressing further
From my own experience:

Why this happening? Why my installation is not progressing further? Because issue is in my network. I connected my system with WiFi and sometimes signal comes with very low quality and in between installation for some second signal was lost and at that time installation is stopped/pushed. That was reason of installation is not progressing further.  But I tapped on cancel but even don't know what will happen! and restart my system and clicked again for installation. It will not be started from begging but started from where we stopped/pushed. Its really good things. And I was write comment like 


  if we canceled installation and restart again then any major problem will occur?


Answer is No you can do cancel and reinstall process any time It will be managed by core system.