Hello, my name is Mark and I will try help you with this.
There is no 100% guaranteed way of removing a stuck glow plug. Much really depends on how lucky you are.
You can try soaking it with penetrating fluid.
You can try soaking it with something like oven cleaner to try dissolve any carbon that may be holding it in.
Another method is to use a low frequency/torque impact tool to try vibrate any carbon loose from the gowplug.
Worst case is to remove the head and send it to an engineering shop.
These tools however aren't cheap.