jobs = jenkins.model.Jenkins.instance.items
oldJDK = jenkins.model.Jenkins.instance.getJDK("JavaSE 8u40")
newJDK = jenkins.model.Jenkins.instance.getJDK("JavaSE 8u45")

jobs.each {
  if (it.JDK == oldJDK) {
    it.JDK = newJDK
    it.save()
    println "updated ${it.name}"
  }
}