You can copyright Batman the comic book drawing; you can copyright photos, images, scripts, etc. from Batman the movie; and you can copyright the *specific* character of Batman/Bruce Wayne, whose billionaire parents were shot in front of him on the streets of Gotham, who had a father-figure butler named Alfred, etc etc. You can trademark the logo on the Batsuit, and possibly even the whole suit if it's distinctive enough.
BUT you cannot copyright stock characters or concepts like "rich vigilante dons black suit and cape to fight crime" or "dapper British spy beds femmes fatales and saves the world." And you cannot copyright costumes (clothing is functional in the US, unless it's so completely unwearable that its only function could be as art). Which is a great reason to put trademarkable things like a logo and unique-looking suit on a character you want to protect.
Let's apply these to this case. What makes a Power Ranger a Power Ranger?
--"Space-looking" spandex jumpsuits suits? Costumes are not copyrightable, possibly trademarkable.
--There are five different colors and white diamonds on their chests? Concepts are not copyrightable. A distinctive 5-color logo incorporating the rangers or some visual element like white diamonds could be trademarked, although the actual logos are all a variation on "lightning-y" words.
--"Power Rangers" and "Mighty Morphin Power Rangers" are certainly protectable (and protected) under trademark. They are too short and functional to be protected under copyright.
--Desire to fight various space assholes who want to wreak nonspecific space evil? Sounds pretty generic...
--Five teenagers fighting together? And they sometimes combine into one big ass robot? That's not even unique amongst futuristic crime-fighting robo-tweens in children's television, let alone all of fiction.
--They.... are one dimensional do-gooders who are so devoid of individual characteristics as to be interchangeable and known entirely by suit color, race, and gender? Now you're getting it! These "characters" are stock at best, meaning they are not protectable under copyright. The individual kids that donned the suits apparently had some half-assed backstories, but a) these too are stock and b) I don't believe the director referenced anything of the sort.