Installing Manga+Press is pretty simple. FTP access to your server. Installation can be handled one of two ways: uploading the unzipped mangapress folder to your plugins directory using the FTP program of your choice, or installing through the WordPress admin(Plugins > Add New). If you need more help installing WordPress plugins in general, see Managing Plugins on the WordPress Codex.
Once the plugin is uploaded, all you need to do is activate it by visiting Plugins in the WordPress admin and selecting Manga+Press for activation.
Updates for Manga+Press are released through the WordPress Plugin Directory, although alpha and beta versions are available from Manga+Press' Github page.