If your tv is old, and no option to instal apps, you can get a Fire Stick, to turn your TV in Smart TV. Its cheap option and works great.
But How to instal Apps in Fire Stick?
Step 1: authorize apps from unknown sources
Before installing a third-party application, you must activate applications from unknown sources. Follow the steps below to activate it:
1: Go to the “Settings” in Amazon Firestick.