You need a compressor. Please don't try to do it without one, it's just not safe. You can buy a compressor, or you can rent them from most auto parts stores for a pretty reasonable fee.
Take it slow, get some help if you can, and be extremely careful. Those springs store an awful lot of energy, and I've seen a lot of too-close-for-comfort calls. If one of those fires off, at best you can hope to only damage part of your garage or car, at worst you lose a limb or worse.