Your Corsa can be lowered in many ways. The cheapest and easiest way it to replace the springs in your current suspension set up to give your car a lower look and firmer ride. There are many Spring Manufacturers incl Apex, Eibach, Pi, etc that do spring kits for the Corsa C. There are often two different kits for the Corsa, depending which model you have. For example, Eibach do a 790kg Kit for the 1.0 to 1.4 Engined models, and a 890kg kit for the 1.7 Diesel and 1.8 Petrol Engines. The reason for this is because of the extra weight in the bigger engines, and the springs are made to absorb this without affecting the ride quality. Get this wrong and your car either won't be any lower, or you will have no softness in the ride and are likely to feel every bump in the road.
You can lower your car a maximum of 40mm using just springs without having to change the struts.
Suspension Kits (Springs & Dampers)
There are several companies that sell complete kits to replace your existing suspension set up. These kits allow you to tailor the quality as well as extending the distance you can lower to 60mm. Again, there are different kits for different models, choose carefully.
Coilover kits are fully adjustable suspension kits that allow you to set the height and ride quality that you want. The adjustment is often a simple twist away, meaning you can have a 30mm drop one day and a 60mm drop the next. It all depends on what you want, and you can set it without the need for a trip to the garage!
Airbag suspension allows you to adjust your ride height with the help of a remote control box. You can take it to the floor if you wish to go that far down!