I'm just trying to get some answers here. Im sorry if this isn't some deep history question about Napoleon's preference for east or west facing toilets. Thank you.
The name was changed to "Teenage Mutant 'Hero' Turtles" in the UK since the British Broadcasting Corp deemed the word ninja to have excessively violent connotations for a children's program. The word, after all means "assassin" and it was a word that was known and understood in the UK with strong negative connotations. Consequently, everything related to the Turtles (comic books, video games, toys, etc.) was renamed before being released in the UK as well as various other European countries.
The lyrics were also changed, such as changing "Splinter taught them to be ninja teens" to "Splinter taught them to be fighting teens". The policies also had other effects, such as editing out use of Michelangelo's nunchaku (which were at the time banned from appearing in any production aimed at children). Fight scenes were often cut to remove excessive violence and funny music added to reduce the impact of the scene.
Other European countries tended to dub the UK rather than the US version for similar reasons. Ultimately, the US was worried that it may lose the European market if it continued to incorporate these elements and the nunchaku were dropped even in the US from series three onward.
Incidentally, this contrast can be seen in other US / UK comparisons. "Family Feud" in the US became "Family Fortunes" in the UK. The reverse happened when "Scrapheap Challenge" in the UK became "Junkyard Wars" in the US.
ref: Cohen, Susan (April 7, 1991). "KID VIDEO GAMES". The Washington Post