Unfortunately gsoap is not binary compatible between releases, so updating it to newer versions in released distributions is not possible, since this will cause all programs that use the existing version to stop working after the update.

You did not give any explanation why you you need a newer version. If it is because of some bugfix in a later version it might be possible to backport it to the version in the distribution in a way that doesn't break binary compatibility. What is possible or not depends on how intrusive the change is. Any change that changes the content of "struct soap" is not possible. Backporting new features is more difficult than backporting bugfixes.