I can't find information anywhere on how to update on OSX? There is no update app feature within the app. I can't see any information on the website. I can download the new versions of Yacreader, which contains yacreader.app and yacreaderlibrary.app. Do I just drag these into the applications folder and overwrite the existing versions? I don't want to overwrite any settings or have to re-import all my comics.

Yes, just replace the old apps and you are done.