You can't do anything, really. People have different opinions on everything. Not everyone is going to agree with your specific views—that's just how life is. Some people like soccer, some like basketball. I hate Nicki Minaj but a lot of other people like her. You can't force someone to change their opinions on something. I for one am someone who rarely changes my opinion once I've set one.
Maybe your friend finds the show girly? (I know I would considering that the fifth season was probably the most advertised) Maybe they think you're too old to be liking the show? Either way, you can't force them to agree with you. Maybe, like Princess-Flora said, show them an episode or two, to see if that could sway then in a favorable direction.
But if they still believe the show "sucks", you can't do anything about it. I love heavy metal but one of my best friends hates it. Can I do anything about it? No, we just move on. They won't dislike you anymore (And you certainly shouldn't dislike them) just because you like Winx and they don't.
Well, I'll show them my top three episodes (A Fairy In Danger, Valtor's Mark and Saving Paradise Bay) and ask them what they think. If they still don't like it, who cares? I'm not controlling their emotions.
Nothing lovebaltor is right if she or he says that it sucks what can we do about it nothing like I say in my article if u want ur opinion to be respected respect others opinions.but if they don't lik it who cares it's not like we can make them like it.and it's not right we can't force someone to like something