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#50
I'm afraid you need a bigger drive. If you cannot free up some more GBs in order to reach that 16 GB it is going to be difficult. Where are your personal files located? Maybe you can move them to another drive and gain some space.
In my opinion 32 GB is not enough for a Windows system partition. I always recommend a minimum of 50 GB for the Windows system. If I where you I'd replace the SSD, get one with at least 100 GB, clone the system onto the new SSD and try again to update Windows.