It is not possible to manage or cancel your subscription within the nugs mobile app. 

If you subscribed in app using Apple or Google you have to use Apple/Google Subscriptions:

For Apple Click Here -- For Google Click Here

Direct subscribers can cancel on the Account page on (login, then click Account>My Account in the top right corner of the page). 

Click Manage Plan

On the next page select 'Cancel Subscription' or switch to your preferred subscription level: