How do I make my HD TV 1080p?

I have a LG 47 in. LCD TV. When I bought it it said that it was 1080p, but on my Explorer 4640 HDC converter box from Time Warner Cable, it says on the HD channels that it's only 1080i. How can I make it 1080p. I want to change it because 1080p is better than 1080i. Do I have to go to the settings and change something? Please Help!