It is still possible to purchase Lightroom 6. It costs $79 in the US or local currency price. Go to this link:
The price of the full version is normally shown at the check-out but you can use the pull-down menu to switch to the cheaper upgrade price if you already own Lightroom 5 or an earlier version. Lightroom 6 is the final perpetual licence and it is no longer being updated by Adobe. So be aware that as modern operating systems get updated there is a risk it could become redundant.
If you wish to remain completely up to date and have support, if needed, its best to subscribe to one of the photography plans starting at $9.99pm or local currency price.
Can I still update to Lightroom 6.14 or is too late? If too late, which plan would you advise to take? Thanks
Make sure you understand that there will never be updates to Lightroom 6.14 — no bug fixes, no features added, no new camera support, no new lens support, and no support if your operating system changes and LR 6.14 won't run (there is already one report that it won't run on the next version of OSX which is OSX 10.14)
If that scares you, you can purchase (actually subscribe) to the current version of Lightroom (as of today, it is Lightroom 7.4) by purchasing the Photography Plan from Adobe. This plan will be updated regularly with new features, new camera and lens support, and bug fixes.
I have LR 5.7.1. Is it possible to update to 6.14 or do I have to purchase the new 6.14 version?
Yes, as in Post#1 by @jon - You will have to PAY (PURCHASE) the UPGRADE to Version 6.0, then Update to Version 6.14
But read Post#3 by @dj_paige for the best advice.