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There are lots of different file managers available on the Play Store that you can use to browse your Android device's root files. Popular file managers include Root Browser, ES File Explorer, and X-Plore File Manager.  You can press and hold on the file and then select "Delete" from the menu that appears. There may not be a su file here depending on how you rooted your device.
Open a root file manager on your device. Find and press /system/bin/. Find and delete the file named su. Press /system/xbin/. Delete the su file here as well. Find and press /system/app/. Delete the Superuser.apk file. Reboot your device.