Install Java agent in JIRA Server

Extract the zip file to a new directory to find agent jar and its configuration files
Open apminsight.conf file in any text editor and add license.key value, which can be obtained from Site24x7 APM Insight page. Refer here to fine tun the agent settings.
For Windows,

Edit the file < installation_directory>/atlassian/jira/bin/catalina.bat to add the following JVM argument

set "JAVA_OPTS=%JAVA_OPTS% -javaagent:{full_path_to_agent_directory}/apminsight-javaagent.jar -Datlassian.org.osgi.framework.bootdelegation=com.manageengine.*,sun.*,org.apache.xerces,org.apache.xerces.*"

For Windows Services,

Follow the JIRA documentation to open JIRA JVM configuration window
Once the window is opened, navigate to Java tab and Java Options field
Add the following arguements (one per line)

-javaagent:[full_path_to_agent_directory]/apminsight-javaagent.jar
-Datlassian.org.osgi.framework.bootdelegation=com.manageengine.*,sun.*,org.apache.xerces,org.apache.xerces.*

For Linux,

Edit the file <installation_directory>/atlassian/jira/bin/catalina.sh to add the following JVM argument

JAVA_OPTS="$JAVA_OPTS -javaagent:{full_path_to_agent_directory}/apminsight-javaagent.jar -Datlassian.org.osgi.framework.bootdelegation=com.manageengine.*,sun.*,org.apache.xerces,org.apache.xerces.*"

Restart the JIRA Server