Microsoft provides a troubleshooting tool SetupDiag that can help determine the cause of a upgrade failure of Windows 10.
Requirements: .NET 4.6
Download SetupDiag.exe, from your Downloads folder double click the SetupDiag program, and if prompted click Yes to approve the program. The program will create 2 files – one is a configuration file and SetupDiagResults.log in the Downloads folder. Double click the SetupDiagResults.log file and choose to open it with Notepad.
This utility only works with Windows 10. The page for the download has additional information on the SetupDiag.exe utility and its parameters.