Will downloading a new iTunes ruin my old iTunes library?

I tried connecting my new iPhone 5 to my iTunes but it said that it wouldn't connect because my version of iTunes was really old (from 2010) and I never updated. It said I need to download a new version of iTunes (10.7 onwards) for it to be compatible with my iPhone.

But my question is, IF I download a new version of iTunes, will all my old songs on my old iTunes disappear? Because if I had to re-download my whole library, I would seriously cry. That would take the rest of my life.

NO! Not at all. Updating your iTunes will not in the least affect your library. Update away.

No. I've tried updating because my iPhone 4 was using iOS 6.1.2 and it didn't really affect my libraries at all, unless you choose to manage it manually.