How to add music that i downloaded for free onto my iphone without using itunes?

My itunes and mac as a whole is outdated so its not letting me add the music through itunes so i'm looking for an alternative way to put the music onto my phone.

"its not letting me add the music through itunes"

My PC is probably older than your mac, so I'm skeptical that age is keeping you from adding any media to your device. If it is, your question should have better described the problem than saying that "it's not letting me."