I cannot remove tv stand so that i can mount on

There are six screws on the back of the set that remove the stand. Turn the set on its face on a soft surface (bed or carpet). At the base of the TV set (on the TV, not on the stand) you will see nine (9) screw heads. Remove the top three and the bottom three. Leave the middle three in place. The stand just lifts off.
Now, replace the six screws into the TV chassis so if you ever want to replace the stand you'll know where the screws are.