Users can always reply "stop" to your message to opt-out from subscription list.
But in the event if you need to remove a subscription from your subscription list manually; follow these steps:
1. Sign-in to the Dashboard
2. Click on "Manage Subscribers"
3. From Subscription lists drop down, select "ALL" or subscription list, from which you like to remove the subscriber
4. Enter the mobile number in Search box and press Search
5. If contact is found, select the contact (checkbox)
6. From "Select Action" drop down, select "Remove from list" and Press Execute.