Storage Space

Hi guys, I replaced my old mac with a MacBook Air. The processor speed is 1.8 GHz; memory 8GB; version; 10.13.3. At the moment, I only have 121.12 GB of storage. When I swapped my old mac for the new one, the guys at the store said that in order for me to keep the 3 years extended warranty I would have to cut the storage space in half to 128. I did it reluctantly just in case something happened.

But the issue I'm having is obviously space. What's taking the most space is my I-tunes. I'll never give that up as I have been a member of I-tunes since around its inception around 2008. And I've always collected music having studied it.

The other issue I'm having: I have an external hard drive. It has a lot of my music there on iTunes but not all of it. When I want to put recently purchased items on it, nothing pops up to where I'm able to.

So any help guys I'd appreciate it.

Greg