Once the Assets are saved in course builder, you can edit/delete it from the Asset Library as well.
Go to Dashboard->Content->Asset Library
You'll see the list of Assets, from the Action section you can either edit/delete the details of chapter items.
Once you click on the details option, a pop-up gets displayed, edit the changes you want to update.
Once you save the changes, the validation message "Successfully updated the changes" gets displayed.
If you update the text you get redirected to the Course Builder option.
If you update the PDF your changes are updated, and you can see them in the Asset Library section.