The ST205 brakes are a huge upgrade from the ST185. The ST185 uses a twin or single pot sliding caliper with a 200 and something disc at the front and a single pot sliding caliper at the rear. The ST205 uses a 4 piston alloy caliper at the front and a 2 piston at the rear with 315mm discs.
However the ST205 setup is not easily transplantable to the ST185 and most people would go for a kit of some type. Something to think about maybe, if you are just wanting to make the car safer for general road use and for an emergency stop then I'd have to question whether it is worth taking the time and money. The brakes are poor but should easily be able to lock the wheels during an emergency stop, if the braking distance is excessive then I would be looking at discs, a higher quality pad, better tyres, change brake fluid and are the calipers in good condition. If you are looking at fast road use and are going to be leaning on the brakes a bit then fair enough look at the kits. The other point is that modern cars have more powerful assistance to the brakes, are you properly burying the pedal in the 185?
Hope that gives you some things to consider.