How to replace Firmware on LG-42LB650T Television with WebOS 5.05.70

I have had this TV for 6 years with No issues. Since about 2 weeks ago when I watch non-HD channels via STB or Wireless the Screen randomly freezes, then goes blank, shows LG screen, and returns, works normally for few minutes till repeats. When I watch HD channels via STB or wireless, It has no issue even if used for few hours. I tried a reset to the initial setting and that did not help. Upgrade said no upgrade found. Has Webos 05.05.70. Is this a hardware problem or a software problem? How Can I replace the firmware? Please advise. Thanks