Apple’s version is an .ibooks (an EPUB with a different container). It is automatically updated on your device when the publisher submits changes. You cannot export the raw EPUB, but for reading on Apple hardware, it is identical to an updated file.
Searching for "unix a history and a memoir epub upd" will inevitably lead to sites like Library Genesis, Z-Library, or various torrents. You will find files named [upd]Unix_A_History_and_a_Memoir.epub. Here is why you should avoid them: unix a history and a memoir epub upd