Did you make changes in template files? You need to transfer changes to a child theme to prevent losing them after lagenda update. Very likely that your problem relates these changes.
Also, it would be better make export theme options in file, before the update (Theme Options > Import/Export > Options > Export Options).
You need to create the child theme and transfer into child theme all files which were changed, read more in documentation http://www.8theme.com/demo/docs/legenda/#!/child_themehttps://codex.wordpress.org/Child_Themes
Custom css code, you need to add in style.css file of the child theme.
The export theme options, that I explained before, only can help you won’t lose “Theme Options” settings if something goes wrong in theme update prosses. Your version of theme is old, so some theme options you will need to set manually, after version update.