Hello,
Here's what i did to get the calendar to start on a Sunday using version 8.2.0:
cd ~/jasperreports-server-cp-8.2.0/apache-tomcat/webapps/jasperserver/WEB-INF/bundles
nano calendar.properties
CAL_firstDay = 0
cd ~/jasperreports-server-cp-8.2.0/apache-tomcat/webapps/jasperserver/WEB-INF/classes
nano relativedate.properties
# 1 - SUNDAY, 2 - MONDAY
week.start.day=1
cd ~/jasperreports-server-cp-8.2.0/
./ctlscript.sh start (or restart)
Clear your browser cache.
It was done on Ubuntu but will also work on Windows.