If you signed up for CBS All Access via iTunes, please do the following:

Apple TV 4th generation & 4K
  1. From the Apple TV homescreen, select "Settings". 
  2. Select Accounts.
  3. Under Subscriptions, select Manage Subscriptions.
  4. Choose the subscription that you want to manage, and use the available options to switch your subscription from Commercial Free to Limited Commercials. 
On Apple TV 3rd generation or earlier (Legacy), you need to use an iPhone, iPad, or computer to manage your subscriptions. 
From your iPhone or iPad:
  1. Go to Settings > iTunes & App Store.
  2. Tap your Apple ID at the top of the screen.
  3. Tap View Apple ID. You might need to sign in or use Touch ID.
  4. Tap Subscriptions.
  5. Select your CBS All Access subscription, and switch your subscription to Limited Commercials.
From your computer:
  1. Open iTunes.
  2. If you’re not signed in, you can do so now. 
  3. From the menu bar at the top of your computer screen or at the top of the iTunes window, choose Account > View My Account.
  4. Enter your password, then press the Return or Enter key on your keyboard, or click "View Account".
  5. On the Account Information page, scroll down to the Settings section. 
  6. To the right of Subscriptions, Click "Manage".
  7. To the right of your CBS All Access subscription, click "Edit". 

If you don't see your CBS All Access subscription but are still being charged, make sure that you're signed in with the correct Apple ID. If so, you might have subscribed on another device, or through CBS.com, and not through iTunes. Please return to that device or CBS.com to upgrade your subscription. Instructions on how to upgrade your subscription on other devices can be found here.