You can get a larger cassette (and derailleur to handle it).
You should end up in your lowest gear when it gets really steep, but don't shift down too early. You will just loose momentum.
I assume you were out of the saddle when it got steep? If not, learn to do that. That's how you get up the really steep stuff. When you are standing you can deal with lower pedalling rpms, so you can go slower with the same gearing than you can seated. You also can recruit your upper body muscles to help turn the pedals.
Beyond that, it's a combination of fitness and learning how to ride under your anaerobic limit. Practice helps both of those. Find a slightly less steep hill and practice on it.