If it is a paid account, simply login and select Subscription in the top right hand corner. There, select Manage Subscription and then Cancel Subscription.
If the account is on Bria Solo Free, simply login and select Subscription in the top right hand corner. There you will see a button below Subscribe Now that says Cancel Subscription. This will remove you from all email lists.
And if the account is still a trial, simply login and select Subscription in the top right hand corner. There you will see a button on the right side that says Cancel Subscription. This will remove you from all email lists.