Hello Jarris
You have to seperate the body-tube from the head (heat may help) and to take out the window.
For this, you have to take out the outer O-ring in front of the window (needle may help).
Then you can try knocking the head (not yours
) to a wooden surface, to get the window out, without damage.
Another possibilty is:
a blob with a hot-glue-pistol and a nail in the middle of the window. After setting pulling out the window at the nail.
When you got out the window, unscrewing the copper heatsink and then the normal modding procedure.
Good luck and best regards
____
Tom