We haven’t had such problem before.
Please show a screenshot where you see duplicate title tags.
Also you need update theme and plugins to the latest versions.
Before update delete “woocommerce” folder in the directory wp-content/themes/legenda/ and it’ll be reuploaded from a new theme package.
To update required plugins download them here http://www.8theme.com/download-plugins/ .
Don’t forget to create back up of your files and database before starting update process!