If you have a CC subscription, then reinstall from the Creative Cloud app. If using a perpetual license, then reinstall from the disc media. The old catalog file should work with the new install.
There is only one way to install it.
Download version 6.0 if you need to.
Install version 6.0.
Enter your Adobe ID or LR serial number into the setup program as appropriate.
Run the update command to update to the current 6.9 version,
or download the 6.9 update and install it manually.