I got my answers.
i used following commands.
-npm update -g ionic or ( use npm uninstall cordova ionic and npm install -g cordova ionic)
or ( npm install -g ionic@latest)
After that I created new project and compared its ionic info with my existing project.All coponents version were same for both new and old project except, New project had higher version of ionic-angular and @ionic/app-script than old so, I used following commands to upgrade these individial components,
-npm install ionic-angular@latest --save
-npm install @ionic/app-scripts@latest --save dev