Step 1 – You should get the latest archive from ThemeForest. You can find detailed description on how to do this in “Getting of Crane theme files” section.
Step 2 – Disable and delete the old theme version.
Step 3 – Install and enable the new Crane theme version at WordPress dashboard or through FTP. You can find detailed description on how to do this in “Theme setup” section.
Your sliders, widgets, content, settings will be saved in database. Deletion of the theme should not affect them.