Upgrade from LR4

Here's the link where you can purchase Lightroom 6:

Adobe Checkout

After you change the option from full license to upgrade then the price will change. Then you will need to go to this website to download the 6.14 update:

Download Photoshop Lightroom

Scroll the page until you see >Adobe Photoshop Lightroom 6. It doesn't look like a clickable link but it is. Click on it and download the 6.14 update. You only need to install the one update, as it is cumulative. That is the only update you will need. There will be no additional updates, upgrades or changes in the future. You will have everything that will ever be provided for your installation.

The latest Lightroom is the Creative Cloud version, it runs on your local computer, and you never have to upload photos to the cloud, but it is subscription, not perpetual license.

If you must have  perpetual license, then you can purchase Lightroom 6.14 (I don't have the link right now, but I'm sure someone will provide it — or you can search the forum for it). Please understand that Lightroom 6.14 will NEVER be updated, it will never get bug fixes, it will never have new camera or new lens support, it doesn't have the latest and greatest features, and if your operating system updates and LR 6.14 won't run on the new operating system, then it won't run on the new operating system and will never be fixed to run on the new operating system.