I have an LG tv and have had the same problem for years. As I figured out the problem was not the tv, but the way I was using it. Which lead to that message of needing to free up memory, made think I had to delete some of my apps to solve the issue. I figured out that like a computer screen with multiple tabs open, your tv will have multiple apps open if you don't close them after use. This is what causes the drain of memory to the tv, and leads to its need to free up memory. So once I closed all of the apps that I had open the message no longer popped up. I now make sure to close the app after i watch it. Closeing the app doesn't delete it from your tv, so no worries. You can open it again whenever you want to watch it. What you do is select the Home button on your tv remote, then select Recent on your tv screen, now close allll of those apps that you have open and are sucking up memory. Remember to close each app after you watch and you will not see that "need to fee up memory " message again. Hope this helps.
C.F.