The uninstall process shouldn't delete any of your Notebooks or Sections.
You may need to reopen certain Notebooks (via File | Open Notebook...) if
they are not automatically re-opened after the reinstall.
There is a built-in backup function (settings for which are found under
Tools | Options | Backup, and the location for the backed up files is
found under Tools | Options | File Locations | Path. Previously saved
backups also won't be deleted during the uninstall/reinstall process.
To be sure, copy all of the files from the Notebook(s) and backup areas
found above before the uninstall. But you likely won't need to recover
from those files after the reinstall.