This article describes how to have Liferay Portal undeploy and remove the previous version of the portlet before redeploying new version of the portlet.
Resolution
Liferay provides a portal.property to address this configuration:
# Set this to true to undeploy a plugin before deploying a new version. This # property will only be used if the property "hot.undeploy.enabled" is set # to true. # hot.undeploy.on.redeploy=true