What did you purchase the Perpetual License version or the monthly subscription version, Creative Cloud?
the perpetual license for lightroom 5.
You probably have the Creative Cloud trial installed. You will have to uninstall that version, this process will not affect your Catalog, Preferences or personal files, just uninstall using the normal process for your operating system.
Download the Lightroom latest version from the link below. Run the installation and use the License key to activate and every thing should be fine.