I have a demo of Sibelius v.1.4 (build 15) for the Mac. Here is the procedure for that version.Command-click somewhere in the measure you want to delete. A double blue lined box appears around the measure. Hitting the Delete key removes the entire measure.
The Sibelius Help file suggests a Control-click for this. That may be a Wintel method.
I do not see enough in Sibelius to cause me to switch from the industry standard in the US - Finale. Some enjoy Sibelius, though, especially colleagues from overseas.
Good luck.