public function upgrade( $version ) {

		if ( $version < 1 ) {
			// Upgrade from version 0 (closed source service) to version 1 (initial open source offering)
			$this->upgradeEcommerce();
			$this->upgradeBookInformation();
			$this->upgradeBook();
		}
		if ( $version < 3 ) {
			\Pressbooks\CustomCss::upgradeCustomCss();
		}
		if ( $version < 4 ) {
			$this->fixDoubleSlashBug();
		}
		if ( $version < 5 ) {
			$this->changeDefaultBookCover();
		}
		if ( $version < 6 || $version < 7 ) {
			$this->makeThumbnailsForBookCover();
		}
		if ( $version < 8 ) {
			$this->resetLandingPage();
		}
		if ( $version < 10 ) {
			$taxonomy = Taxonomy::init();
			$taxonomy->insertTerms();
			flush_rewrite_rules( false );
		}
		if ( $version < 11 ) {
			$this->migratePartContentToEditor();
		}
		if ( $version < 12 ) {
			Container::get( 'Styles' )->initPosts();
		}
		if ( $version < 13 ) {
			$this->upgradeToPressbooksFive();
		}
	}