Either via Locus Map app or via Google Play.

• open the main menu > My Premium
• tap Cancel subscription by the actually active item:
  

• open the Google Play app > your user profile > Payment&subscriptions > Subscriptions
• select Locus Map 4 Outdoor Navigation
• tap Cancel subscription:
  

You can unsubscribe any time.

Even though you cancel the subscription you can enjoy its features to the end of the subscribed period.

If you don’t cancel it, the subscription renews automatically.