I have Lightroom 5 installed on my iMac computer. I installed this program from a disc, and do not subscribe to Creative Cloud. I find Lightroom 6 Upgrade download for SE Asia countries on the Adobe web page, but not for the US. Not sold in the US? Or is it available from Adobe or elsewhere?
Here is the link from where you can order standalone Lightroom 6 upgrade :
Click on Buy next to Adobe Photoshop Lightroom and choose the upgrade version.
Once you have purchased it, it can be downloaded from this link :