I use spotify to sync my local files to my iphone. My local files aren't from itunes, they're just saved onto my computer in a folder. I used to have a dell, and had all my songs on that computer and synced them to my phone. However I recently just got a mac, and I've downloaded a few more songs. I was able to sync my phone to my new computer, and instead of replacing my library on my phone, it added to them (exactly what i wanted it to do). However, now when I download more songs to my new computer and sync them to my phone, the bar at the top of my computer screen that says how much space is used is almost filled up. Most of the songs I have on my phone are old and were downloaded to my old computer, and I don't listen to them anymore. They don't show up in my library on my new computer, so I can't delete them. I do still have my old computer, but I haven't tried to delete songs off of it. Is this what I have to do to get more space? (The picture attached is the bar I was talking about)

Sorry if this seems like a dumb question!