If you have a newer TV, there's a good chance that you can change the screensaver directly on the TV itself. To do this, start by finding the settings menu. This is usually done by pressing the Menu button on your remote control. Once you're in the Menu, look for the option labeled Screensaver or Screen saver.
If you don't see this option, it's possible that your TV doesn't have a built-in screensaver feature. In this case, you'll need to download a screensaver app from your app store. Once you've downloaded and installed the app, follow the instructions provided by the app to set up your new screensaver.