I would delete the book on the blurb site and upload the revised version.
Make changes to book after it's uploaded (revise or upload new version)
Since there is only a note about revising books on the blurb FAQ using "BookSmart" (https://support.blurb.com/hc/en-us/articles/207795516), I'd like to add this as generic thread about updating a book by uploading it again. The behaviour is actually the same for the InDesign plugin, but I could find no information about it, so that's why I contacted the Blurb support.
This is not a question, just information that I got and that I'd like to share:
My question was: What will happen if I anew select "Upload book" from the Indesign plugin? I've made some changes in my InDesign document and want to update or replace the version already on Blurb.com.
Will uploading again replace the current revision of my book or create a new one? Do I need to change its name? Should I manually delete the book from Blurb first?
The answer (from Blurb support Nov 7th 2016) was:
"It will not delete the one you have, or replace the file. There will just be another version that is uploaded to the dashboard of your account. If they have the same title, you can tell the difference by the date of upload or even page count if that has changed."
I think this is good. I can delete the old version myself, if I don't want it.
Edit: Now that I actually did this... Uploaded again, I got a question from the InDesign plugin, whether to replace or keep the existing version! So the answer from Blurb Support seems to be wrong.
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I have had terrible responses from Blurb. I'm disappointed. Either they don't answer my question at all or, as here, there is a questionable solution. Wish they could get this part of customer support right!