Step-1 : Download the greenball plugins from jenkin's plugin download section. Link-https://wiki.jenkins-ci.org/display/JENKINS/Green+Balls. Then click on the archive link.It will lists all the versions of the plugin.Click on the latest. It will be downloaded as greeball.hpi.
Step-2 : start jenkins. Once it is available open jenkins
Step-3 : Go to Manage Jenkins.
Step-4 : Click on Manage Plugins.
Step-5 : Go to advanced tab
step-6 : Go to upload plugins section
step-7 : Click on browse and select greenball.hpi
Step-8 : Click on Upload.
step-9 : Once done. Restart Jenkins
Step-10 : Done .Now you can see all blue balls got replaced by green balls.
Just to make double sure:
Step-1 : Go to Manage Jenkins.
Step-2 : Click on Manage Plugins.
Step-3 : Go to Installed tab
Step-4 : You can see green plug in is listed here.