If TV is too old to install apps on to like modern TVs but has a free Hdmi input and you also have WiFi can use your phone by getting Google Chromecast.
If you have a phone capable of using Chromecast it can cast to your tele over your WiFi network and then to your Tv via a Hdmi dongle. YouTube supports Chromecast.
A PC/Laptop mentioned above is also viable, just connect it with a Hdmi cable.