In some cases it can be necessary to delete a single ERSA or DAP page and have it re-download (if it was somehow corrupted). To delete a single page, open the Terminal tab, and tap the book icon at the top right.
Find the page which needs to be deleted, and swipe the row in the table. A delete button will appear. Tap delete and any saved page will be deleted.
When the page is next accessed, it will be downloaded and saved again.