Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble, Sharon.
You will need to open up the tv, remove and clean the filter. This is, generally, not considered a task for the end user. It is not as simple as changing a lamp for example. This is something that would be recommended to have a service tech come out and do for you, as the back has to come off, access the filter which is near some high voltage and other sensitive components, and requires entering a special service menu to reset the filter error/counter. You could expect this type of tune up service to run about $100-150 to have a tech out to do this for you.
If you want to try yourself, the filter is behind the back cover at the lower right corner (when facing the rear of the tv)..
At this point, you may even want to consider replacement as an option rather than investing more in a tv this age which is well past its service life at this point, and will only continue to need further parts and maintenance. You could get a brand new LED tv with a better picture and fresh warranty in the $300 range these days.
Let me know if you need more info, help finding a repair shop, etc.