For noobs it might be good to expand on two instuctions in the OP (i.e. how to get plugins working after updating from 64bit to 32bit build).
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How to "Delete your old packages directory":
System -> Appearance -> file lists -> show hidden files and directories and allow file deletion
System -> File Manager -> add source (call it "Root") and browse/add the location:
/.kodi/addons/packages
Then open it, long press any file there and choose "Select all". Then long press again and choose "Delete".
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How to "Refresh the repos":
Delete this file: /userdata/Database/Addons20.db
Reboot.
System -> Addons -> press left to bring up the side menu then click "Check for updates"