The best way to do it is to buy a real cheap soldering iron (3Euros) and heat the three points at which the battery is soldered to the botherboard. While you heat each one of them, the according battery leg will go loose and you will be able to pull it out of the solder hole. The A2000 is probably the most convenient Amiga when it comes to replacing the battery, as there is not much in terms of components near the battery.
