If you want to upgrade the Angular CLI version of your project you may run into tough-to-fix errors and bugs from simply changing the Angular CLI version number in your project. Also, because the Angular CLI hides a lot of what's going on in the build and bundles process, you can't really do much when things go wrong there.
Sometimes the easiest way to update the Angular CLI version of the project is to just scaffold out a new proejct with the Angular CLI version that you wish to use.
Because Angular 2 is so modular and encapsulated you can pretty much just copy over all of your components, services, pipes, directives and then fill out the NgModule as it was in the old project.
ng new NewProject
ng init NewProject