How to remember and update songs in your head?

Do you know how people could remember songs which are current and remember them forever in their mind, but without them having to purchase them or keeping them in their ipod?

I love updating my knowledge of current songs, however I usually have to download them illegaly because that would be a lot songs to purchase, but I usually pay for the ones I love.

But if purchasing is not an option, how to remember the songs i’ve heard or come across?

I notice that some people just know the current songs without having them purchasing it.

do you know any tricks? thanks