Deactivating your Roku account is easy!
But before you do, keep the following in mind:
By deactivating your Roku account, you will lose any purchases that you have made from the Roku Channel Store, such as games, themes, screen savers, etc.
Also, make sure to manage/close any subscriptions to channels you may have, as your subscriptions will not end automatically after you deactivate your Roku account.
Knowing the above, if you'd still like to deactivate you Roku account, just go to my.roku.com and sign into your account. On the Account page that appears, just scroll down a little and under “Account Management” you’ll see “Deactivate Account”.