There is no trial for Lightroom 6. The trial you want is for Lightroom CC, if you use that and find it does what you want and decide to purchase it, then you can convert it to LR 6 and not have any Creative Cloud features. By installing it, you have access to the Creative Cloud features for 30 days free (of course, you don't have to use any of the Creative Cloud features like Lightroom mobile and you can turn it off if that's what you want). And by installing it, you are not subscribed to the Creative Cloud, you are using the free trial. If you decide you don't want to purchase Lightroom 6, then just uninstall the trial.
The download/install is the same for LR6 and for LR CC 2015.
To buy the standalone license, got to the Adobe product page of your country, scroll down to LR, hit buy and select the upgrade.
To license the software follow this: https://helpx.adobe.com/lightroom/kb/serialize-lightroom-cc-trial-to-activate-as-lightroom -6.html
Thanks for clarification. I just wanted to make sure not to mess up my existing perpetual license or end up paying for the cloud which I definitely do not want.