Hi how remove this switch?
I would like to help you but , from your pictures it looks like a "very" budget Chinese light .., most of these have the assembly of the switch fit pressed in the body of the tail cap ! Yours seems to have this assembly made of brass (not plastic , that is more common ) , and due to the fact that has no holes in it ( used to insert a long nose pliers and to unscrew it from the cap ) leads me to assume that is pressed fit and , maybe , glued ...
If you are sure that the switch is the problem ( I think that you already measured it !) , the only chances you have to remove it are , as follows :
1.Make 2 small holes ( 1.5-2 mm) at 180 degrees , in the outer brass ring . Not very deep , but enough to slip in , the long nose pliers .Twist it , CCW , and if is moving , you can take it out . Anyway , looking closer to your picture I do not see any threads under the ones for the body... Another possibility is that the small holes for unscrewing , to be on the other side , next to the rubber boot .., if so , try there , doing the same CCW movement...
2 . If this light is a dear one , and you want to repair it , this second method has only 50% chances to success ..!
You'll have to try to press ON the rubber boot , with a small piece of hard wood , hammering it , or just using a vice .., if is fit pressed ,the brass will just pop out , giving you the access to the switch... Most of the times , this method ruin the original switch or even the PCB under it , so , use precaution and common sense...
If you succeed to take it apart , look carefully how the original switch was standing in there ( most probably ,one connection of the switch is soldered to tail PCB and the other one is pressed by the brass ring , towards aluminium tail cap body ).
And do not forget : sometimes , the price of a quality switch is higher than the price of a new light !...Does it worth it ? You know better...
Good luck !
thank you for careful explain
there is a problem with no threads around switch 
is not expensive but isn’t cheap chinese light:
Sorry , you're right , is not a cheap one !..., but , if there are no threads is clear that is fit pressed and , maybe glued...
An other option , could be a gas blow torch , heating around the tailcap , slow and moving the flame all the time , but only from the out side .
Aluminium expands about 4% , twice more than brass , the heat will soft the glue ( if it is any ) and tapping the rubber boot , maybe, will make them disengage .
Anyway , the boot and the switch will be compromised...
Or , as was doing many years ago , on the lights with such kind of fit press switch : 1-2 ml of contact cleaner ( plastic safe !) , injected with a syringe thru the rubber boot inside the cavity where the switch is , click the switch few times , and leave it in open position ( to allow for the cleaner to work on the contacts) , a night or so , until the fluid evaporates. Could be a good chance to recover the assembly , without open it ... Give it a try...