Windows 10 Upgrade Assistant is stuck at 99% – 1. Copy the Media Folder From C:\$GetCurrent\
Unplug peripheral devices. Temporarily disable your Internet connection.
– How to Fix a Stuck Windows Update Assistant and Rescue Your Update
Perform a clean system reinstallation. Windows 10 Upgrade Assistant is stuck at 99% · Open File Explorer, type C:\$GetCurrent, and then press Enter. · Copy and paste the Media folder to the desktop. Windows 10 update assistant stuck · Change the location of the Media folder temporarily · Disable the Windows update service · Delete Windows.