The easiest way to know if your TV is 4K is to look at the user manual or the packaging box that shows the display details. Usually, user manuals term the resolution as Ultra-High Definition or simply, UHD. It might also be denoted in terms of pixels, 3840 x 2160. Alternatively, you will find ‘4K’ written in a bold text format.
You can also check the model number written on the TV, or on the back of the TV, and search about it on Google to find its specifications.