Hello,
What version of SEPM are you running?
The Article link which you have provided you is for the SEP 11.x.
If SEP 11.x is the product for which you are looking for then open the DVD for the SEP 11.x and then either go to SEP folder OR SEPM folder and look for "lusetup.exe"
OR
Find it on Symantec FTP site: ftp://ftp.symantec.com/public/english_us_canada/liveupdate/3.3.0/
Secondly, In case for SEP 12.1, you can check this Article:
How to Uninstall and Reinstall LiveUpdate on SEPM 12.1 (Enterprise Edition or Small Business Edition)
http://www.symantec.com/docs/TECH171060
Windows LiveUpdate Client for Use with Symantec Endpoint Protection Manager 12.1
http://www.symantec.com/docs/TECH181305
Hope that helps!!