The update is said to be an industry-first wherein the signal bars represent the real phone antenna performance, and not just a nice graphic as in the past. Mind you in the past a nice graphic was all that was needed, but in the light of antennagate Apple thought that some physics and engineering might deflect the perception. That's an odd twist for a "brand image" company, but in any case having a "real" set of bars is good. I suppose 1 bar is half the strength of 2 bars etc, or at last some formula between them. 

I'm not sure what the formula is, although that's sure to be published soon. In this case I just lay two phones beside each other and took screen shots. One was upgraded, and the other not. The upgraded one shows 2 bars, and the old one 5 bars.