Please do following step for update.
1. Download latest version from themeforest and extract in your local. You can find travelo.zip file in it.
2. Activate another theme in administrator in your website.
3. Delete travelo theme in your website via ftp
4. Install Travelo theme latest version in your website and activate it.
5. Install/Update required plugin in Appearance -> Tools menu or Travelo -> Tools menu.
Before updating, we recommend backup your website.
And to check file change log, please read readme.txt file in Travelo theme folder.