When a song is playing and you see the standard display (cd cover, artist, album title, progress bar, time in, play state, time remaining, clock & battery sate), press the center button once for graphic equalizer, again for centered larger cd cover picture (the bit you're asking about), again for most standard display info plus 'next song', and again to return to standard display.
I don't know of a way to bring up the centered big cd cover display as default.

-webbit