To deactivate your Plays.TV account, just log into your account on the web, then go to the Edit Profile menu, which you can find by clicking on the dropdown menu on the top right of your screen. From there, you'll be shown the Basic Info page and there is an option to deactivate linked at the bottom of the displayed area.

When you select "Deactivate Account", you are then prompted to enter your password and confirm the action, at which point your deactivation should be complete.