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 nugs.net subscribers can cancel on the Account page on nugs.net (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: