Bookle 1.0.4
Stairways Software has released Bookle 1.0.4, the EPUB reader for the Mac that was developed in collaboration between TidBITS’s Adam Engst and Peter Lewis of Stairways Software (see “Introducing Bookle, an EPUB Reader for Mac OS X,” 6 February 2012). This update fixes a small glitch with the initial selection of some books, expands the range of the font size selection to 160 point for those who want really large font sizes, and adds support for invalid EPUBs with unencoded spaces in their table-of-contents references. The new release also defaults to UTF-8 to fix some character display issues and adds tips to the toolbars for better VoiceOver
support. ($9.99 new from the Mac App Store, free update, 2.6 MB)
I don't see an updater for 1.0.4, I have 1.0.3.
Look in the App Store app's Updates tab - it should be there, like all other Mac App Store application updates.