there should be a cople of grub screws in the trigger itself that can do this. usually pre and post travel. pre travel is the amount of travel before the switch activates and posst travel is the amount of travel after the switch activates. just work out which bit you wish to shorten, smack a suitable allen key in there and twiddle till it feels good (ooh)
if it doesnt have adjustment screws (and not owning one i couldnt say either way) the job is much more complex, namely involving driling, tapping and fitting said grub screws and then doing as above
rich