When updating SketchUp to a new version you can copy all Classifications, Components, Materials, Styles, and Templates. You can even migrate your extensions using the Extension Migrator extension.

The Extension Manager in SketchUp and the My Extensions page in Extension Warehouse can help you manage, update, or uninstall the extensions you’ve chosen to use.To enable or disable extensions on the Home tab, use the toggle next to each listing. You can also enable or disable all extensions using the Enable and Disable links at the top of the window.

SketchUp and the Extension Warehouse were made to work together. The most common way to start looking for extensions to customize your SketchUp workflows is while you are using SketchUp.