Canceling Robo Shield depends on how the product was purchased.
Robo Shield purchased from the App Store
Remember that canceling Robo Shield, will also cancel your premium Hotspot Shield account.
Apple's policy requests that you cancel your subscription through them directly. We cannot cancel iTunes subscriptions. Before canceling your subscription, please ensure that you are signed in to the same Apple ID with which you originally purchased your Premium subscription.
To cancel your Robo Shield account, please read the following article.
Hotspot Shield (and Robo Shield) was purchased from the App Store
In this case, Robo Shield is bundled with Hotspot Shield. By canceling Hotspot Shield Robo Shield will also be removed from your account.
Please read the following article to cancel Hotspot Shield.