Please, do the following:
1. Perform settings backup under Cherry > Options. Just scroll to the end of the page and locate the Export button.
Make sure you have Cherry Data Manager plugin included.
2. Backup your theme files (wp-content/themes/monstroid directory).
3. Delete Monstroid theme from Appearance -> Themes section in admin panel.
4. Download theme archive and follow Manual Installation to install new version of Monstroid theme or
5. You can use Monstroid Wizard (Tools > Monstroid Wizard). Make sure to delete Monstroid Wizard plugin and reinstall it from this link before update.
6. Import your updated files from the backup and import Cherry Options if required.
or use this link:
http://www.templatemonster.com/help/quick-start-guide/wordpress-themes/monstroid/index.php?lang=en§ion=installation#update-monstroid