How to clean neglected DIRTY stove & grease filled kitchen wall?

Get a clean towel and just wet it and give it a good wipe over, then put some good old 409 on it. Get a plastic putty knife, you will probably need a small and large. Just spray the 409 on and start scraping away. This will remove a lot of the grease. You may have to go over it a couple of times. Let everything dry, then do a final wipe with white vinegar.

It would be just an experiment but you might try the product awesome. You can get it at dollar general. Be careful and try just a small spot first . You can dilute or use full strength. Directions on bottle. I've found it to be a good product.

Put your mask and gloves on and get your elbows ready. I would start with any degreaser of your choice and go for it. I like vinegar but from the sounds of it, you need to go stronger. For the walls - all the walls (probably throughout the entire home), use TSP, that will clean anything, might even try on the stove . . .

http://www.apartmenttherapy.com/how-to-green-clean-grease-from-138621

https://www.remodelaholic.com/45-quick-cleaning-tips-holidays/

http://cleaningtutorials.net/2016/05/remove-grease-stains-painted-walls/

This calls for a different type of grease...elbow. Use powdered cleanser (always dampen it before scrubbing) on the stove. Use any type of spray cleanser you have that will cut grease. Have lots of old cleaning rags, brushes of various sizes, container or bucket for water. You'll be very happy with the end result.

Try Blue Dawn to clean it.