There are 3 ways you can get to know what all has been changed in the latest version.
1. Forums : Open the Issue Log : http://vibethemes.com/forums/forum/wordpress-html-css/wordpress-themes/wplms/7309-issue-log
2. ThemeForest main page : Scroll down to the bottom to view the Issue log : http://http//themeforest.net/item/wplms-learning-management-system/6780226
3. Your Own site : A changelog.txt has been added form version 1.3.4 which is the full log file from the development repository, you can access it from here http://vibethemes.com/envato/wplms/wp-content/themes/wplms/changelog.txt or http://yoursite.com/wp-content/themes/wplms/changelog.txt
You can also check what all has been changed via following below Links :
WPLMS : Theme : http://vibethemes.com/envato/wplms/wp-content/themes/wplms/changelog.txt
Vibe Custom Types : http://vibethemes.com/envato/wplms/wp-content/plugins/vibe-customtypes/changelog.txt
Vibe Course Module : http://vibethemes.com/envato/wplms/wp-content/plugins/vibe-course-module/changelog.txt
WPLMS Events : http://vibethemes.com/envato/wplms/wp-content/plugins/wplms-events/changelog.txt
WPLMS Assignments : http://vibethemes.com/envato/wplms/wp-content/plugins/wplms-assignments/changelog.txt