This may sound silly but are you sure you have administrator permissions? (Logged in with an account with Administrator privileges.)
If you are sure you have the correct permissions, you may also want to check with the original theme developer to see if there are white label admin features enabled within the theme. You will need your client’s login to communicate with the developer of a purchased theme on ThemeForest.
White label options would be most commonly located in the theme’s functions.php file (or a similar named file – so check your includes) and would look similar to the example in the below link:
http://www.wprecipes.com/how-to-remove-menus-in-wordpress-dashboard