Error occurred while updating my Windows 10

My PC was running low on space and Windows recommended me to add an external USB drive in order to complete the updation process to version 20H2. I started downloading the update, and when it hit 100%, it gave 'Download error' and now when I click 'Retry', it starts all the way from 1%. I still have the folder named WUDownloadCache in my USB drive occupying around 3.9 GB space. Is there a way to use that folder to update my system? Or, do I need to start all over again from 0%?

Question by user871532 on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.