Complex sentence: TV-am replaced "TV Mayhem" with "Cartoon World", which as the name suggests showed just cartoons, which ran from November 1991, until TV-am's demise in December 1992.
Split into simpler sentences: TV-am replaced "TV Mayhem" with "Cartoon World", which as the name suggests, only showed cartoons. This ran from November 1991 to TV-am's demise in December 1992.