The latest version of Lightroom 6/CC.
If you want to upgrade to standalone version, you can go for Lightroom 6 at $79 : Products (only if you have a previous Lightroom version)
Or, you can go for subscription of Lightroom at $9.99 per month : Creative Cloud pricing and membership plans | Adobe Creative Cloud
You can download the same version that you are using now from the following website:
You will probably have to change regions at the bottom of the page.
If you want to upgrade to Lightroom 6, here is the link:
After you indicate the version that you have been using, the price will change to the upgrade price. Again, you will probably have to change regions at the bottom of the page.
If you decide to upgrade you will need the serial number from your previous version as well is the serial number from the upgrade.