There's only one way to get that TV to switch from 480i (which is an SD or Standard Definition signal) - that's to provide it with an ED or HD resolution signal (a 480P signal is often called ED or Enhanced Definition while 720P, 1080i and 1080P signals are called HD or High Definition).
The old standard yellow composite video cable.
You will not get ED or HD signals through the old composite RCA phono jacks (usually yellow in color), either. You'll need to use an RGB (red, green and blue) component video cable, HDMI cable, DVI, or other type supported by both your TV and the video source (CATV box, Blu Ray disc player, Satellite converter, etc.). More on this, later.
An HDMI cable - this provides Digital audio signals, too.
A DVI cable.
First, you'll need a source capable of sending ED or HD signals. This can be a progressive scan DVD, Blu Ray player, HD Cable or Satellite converter, or a simple TV antenna. Not all DVD players are capable of the 480P progressive scan output - it must be labeled as such. The DVD movies are not labeled progressive scan as they all will play back at 480P if played in a DVD player capable of progressive scan, otherwise they play at 480i. A stand alone Blu Ray player or one in the Sony PlayStation 3, the older HD-DVD in the Xbox360, (it is important to note that the Nintendo Wii can output either 480i or 480P signals only when connected with their special component video cable), "set top boxes provided when you choose HD service from your local cable provider or satellite TV provider are the main sources for signals better than 480i. As mentioned above, the old standard yellow video jack is not capable of supporting signals better than 480i. You must use the HD jacks and cables between to get these signals into your TV.
The Wii 480P cable assembly - includes stereo audio, too.
Lastly, if your TV has an ATSC tuner (it is not uncommon for it to have an NTSC tuner and CATV tuners as well), you can input a UHF antenna directly into the the antenna terminals on the TV. Broadcasters in most areas have been moved into UHF bands - but some areas have one or two that operate in the VHF bands still. Check antenna web
for information and help selecting antennas and broadcasters in your area. The nice thing about the antenna method is that no other cables, converter boxes, etc are needed to enjoy HD signals - plus - they're free!
Just remember you need a source capable of ED or HD signals and a way to get those signals to your TV. The yellow composite cable is from days ago and only passes 480i signals.
I hope this helps and good luck! Please take a moment to rate my reply - thanks!