The only method available to go back to the original version of Windows installed on your PC would be if the PC manufacturer provided a utility to roll your system back to factory settings, however, that process would wipe all your data on installed software.
The best option to stabilize your system and fix Windows updates is to open the Settings app.
Go to System - Recovery.
Click the 'Reinstall Now' button in the 'Fix problems with Windows Updates' section, then wait for that process to complete.
This process will not affect your files, settings or installed software.