deleting old installs of windows question

Keith S

My computer originally came with windows 7 or 8, not sure which one.  I took the option to upgrade ton windows 10 and a friend did it for me.
I heard that an update of windows from an earlier version can still have traces of the old OS installed on it (broken files, files that direct to functions that are no longer there)
If this is true, where or how do I uninstall or remove these remnents?
Also, I saw on this list taht when you update jaws, the previous version is still kept installed, incase you need to go back and use an older version if the newer version of jaws is well, glitchy.
How would I go about removing the older versions?

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