WE 3.8 Baby Hi-capa hammer springs

[Paul S]

I have the above pistol which has stopped working, when fired the hammer goes forward and stops against the valve in the mag but dosent have enough force to open it, if you push it forward with your finger it fires, I have tried several mags and it is the same. I was told it is a weak hammer spring is this correct? and how do you change it?
cheers
paul