904 Transmission 1-2 shift control valve spring install help.

Ok, evidently this is fairly common but my 1-2 shifts are way lower than my 2-3 shifts. I like where my 2-3 shifts are but my 1-2 shifts are about 1000 rpm too low. I've read this is likely from a weak 1-2 shift control valve spring. Does anyone have any pics of where this is located and instructions on how this is accomplished? Can this change be accomplished fairly easily? I've never done any tranny work except filter and fluid so this is all new to me. Thanks!