Am I installing High Sierra correctly?

[Appletise]

I downloaded High Sierra update and had my 4 TB USB hard drive(ExFat) attached downloading from iTunes. I chose to update my Sierra to high sierra, selecting my MBPR SSD hard drive as opposed to the 4 TB USB hard drive that was attached. It has been over three hours and nothing appears on the screen also the back Apple Icon is lit and my attached hard drive has its little LED light flashing as if operating. Should I just let it continue or keep the on off button on the top right down to force shutdown? I know I should've disconnected my USB hard drive first I think, because I'm slightly worried its contents might be deleted.

 

[Fishrrman]

If you're able to get out of where you are stuck now, I'd suggest this:

Get a USB flashdrive 16gb or larger.
Get one of the following:
- Boot Buddy
- DiskMaker X
- Install Disk Creator
(all are free)
- Use one of the apps above to create a bootable USB flash drive with the installer on it.
- Boot from the flash drive and try the install that way.