What you need to do depends on the client you use. You may not need to do anything if you use, for example PHP. You may need to recompile your code if you use, for example, Axis. It is advisable that you empty the cache in which your WSDL data is stored.
During the day of February 2, 2012, we will be changing the SOAP interface that is found at the url https://ssl.ibanrechner.de/soap. To determine the exact point in time of your update, we suggest that you change your url to https://ssl.ibanrechner.de/soap-12-2 before February 2. This url holds the current version. After February 2, change the url back to https://ssl.ibanrechner.de/soap - that way you'll point your software to the newest version.
If you do would rather keep using the current SOAP interface beyond February 2, 2012 instead of updating your client software, there is just one thing you need to do: use the URL https://ssl.ibanrechner.de/soap-12-2 instead of https://ssl.ibanrechner.de/soap . You can do so straight away, there is no need to wait until February 2. We do not plan to remove the soap-12-2 version. If, however, it would ever become unavoidable to take the soap-12-2 version down, we will let you know via the newsletter.
If you want to use the new features immediately rather than wait until the next update, use the URL https://ssl.ibanrechner.de/soap-ce. This version might change more often and without warning.
This is the preliminary date for the next update. Since we have no feature requests yet, it is not yet clear that there has to be an update at all at that date.