I just upgraded last night and didn't have any problems by just replacing the old folders (attforblock in mod and attendance in blocks) and putting all the language files in their appropriate location.
I upgraded from 1.8 to 1.9 though so I'm not sure if your situation is different or not. Changes made to tables for me going from 1.8 to 1.9 should be made for you as well when upgrading if they are necessary.
How to upgrade it to version 2.0.4?
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