Ensure that your locker is empty before doing this, as you will lose access to it after canceling your subscription. Sharebox+ subscription have no binding time, you can cancel your subscription at any time you want.
Android:
Step by Step:
Press the menu to the left.
Press manage subscriptions.
Select the subscription you want to cancel.
In the right corner press the trash can to delete your subscription.
Press "Yes" to cancel it.
iOS:
Step by Step:
Open the reservation you want to cancel
Press "More" in top left of the screen
In the list of choises that appear press "Stop subscription"
A Stop Subscription popup appears and you are asked to confirm.
Hit the red confirmation text to stop the subscription.