at the top of the spring guide, is a flat part that rests in the notch on the inner barrel. look VERY closely, there is a retaining pin there. tap it out carefully, while holding the spring back with vice grips of some sort.
part # 33 in this diagram is the one i am talking about.
may i also reccomend you get the RCC Recoil Spring Guide as it disassembles with no tools, and allows you choices with spring control (using both PROUD springs will likely not put the gun in battery once a mag is empty)
YouTube - my recoil rod and spring