Yes, if you use a legal version of Ligrhtroom 6 or Lightroom for Windows 7, you can always request an update. Yes, you can use the free trial version available on the official website or read my review on how to get Lightroom for free. You will get a licensed product without spending money.
If you have a license key, but the disk was lost, downloading Lightroom 6 for free through the official website will be a great way out.
For you not to examine all sections of the website, while trying to get Lightroom 6 standalone, I provide a direct link to download this Lightroom version. Finding Lightroom 6 free download link can be a challenging task, as developers specifically hide the download button.