Depends a lot on the model of TV.
It may have a in-built HD tuner and get it automaticaly in you are in an HD area.
It may need a feed trom a 'HD set top box' to feed it from freeview of freesat.
Give us the model number and we might be able to narrow it down.
How to watch Wimbledon 2015 live online: follow the tennis from your laptop or PC