After installing iReport 5.6.0, disconnect the machine from automatic Java updates. A silent upgrade to Java 11 will break your report designer instantly. For production report design, consider running it inside a Virtual Machine snapshot.
Here is the first major challenge you will encounter. If you go to the official Jaspersoft Community website today, you will not find a direct link for "iReport 5.6.0." TIBCO has removed legacy binaries to push users toward modern tooling.
: iReport reached its "End of Life" in December 2015. While it is still available for download to support legacy JasperReports, it is no longer receiving updates or bug fixes.