Thanks for the prompt reply. I get an error message saying i cannot install the software.
Lightroom CC/6 update – January 2016
Installation failed. Error Code: U44M2P7
Do i need to un-install the current version (6.5.1) before installing version 6.4?
Thanks again. Tom
Yes, if you are looking to rollback to a previous minor version, you do need to uninstall and reinstall.
If you were looking to install version 5.x, that would work fine as a side by side install.
If you looking to re-install the same version of Lightroom, then yes uninstall Lightroom 6.5.1
restart the machine
Then follow the link to download Lightroom 6 : Install Photoshop Lightroom
Now you can update the software to the specific update, refer the download link for 6.4 update.