How can I find out what headset I have

I want to replace the headset on my bike but I don't know what type I have apart from it says cartridge system inside and the bearing is pressed in to the frame. So would anyone what type I have or know of any good bike forums that don't tell you to go to the local bike shop.
If I remove the red circlip in the picture the centre cup comes out with all loose ball bearings.


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