Let's face it. Superman isn't really seen as cool, yet other characters like Batman are. But, why is this? I'd wager my entire life-savings that The Dark Knight Returns helped to some extent and then The Dark Knight trilogy boosted Batman's popularity. But, what can be done to Superman to make him cool?
Maybe make him grittier?
KC Superman proved to be a grittier portrayal of the character, he still wore his underwear on the outside yet it was still a serious story. This version of Superman had been shaped by the events of destruction and chaos. Kingdom Come proved to be a popular story and was instantly regarded as a classic, some regard it as the greatest Superman story ever.
Make him hold back less?
Superman is constantly holding back. It's a fact, maybe too much as times. So, why not loosen his morals? I feel that his morals heavily restrict his character, we get that he was raised on Earth but he needs to let go a bit more. When holding back, he struggles, but when he lets go we see a true warrior. Maybe this will appeal to a younger audience?
Superman actually didn't win this fight, but physically he was creaming Darkseid. We need to see more of this.
Take away some of his powers?
Some of my friends, who have no knowledge on Comics whatsoever complain that Superman has too many powers. There is no point arguing with them, but if it really will help, maybe his power-set should be altered to something similar of Captain Marvel. That'd atleast make things simpler, one could argue that Superman doesn't use his powers but sometimes there is just no point.
These are just a few methods. I'm sure their are plenty more, but this is just my opinion. Be sure to mention others: