After you install Lightroom CC and start the new program, it will find your existing catalog and prompts you to upgrade it. After the catalog is upgraded all of the work that you have done will be in the new catalog and you can continue working as you have been. When and if you decide that you no longer need Lightroom 5 you can delete the old catalog. But I would recommend keeping a backup of the old Lightroom 5 catalog just in case.
thanks very helpful. John
You do not have to re import the images in Lightroom CC.
You can simply use the same Lightroom 5 catalog in Lightroom CC.
When you upgrade to a new version of Lightroom and open a catalog from an older version, Lightroom upgrades the catalog automatically. The old catalog remains untouched. The new, updated catalog contains all of the metadata associated with the previous catalog and photos.
For more information check the following link : https://helpx.adobe.com/lightroom/kb/catalog-faq-lightroom.html#main_How_do_I_import_my_Li ghtroom_2_catalog_into_Lightroom_3_