Change a tangent weight

[birdey]

Hi, all. I want to change one of tangent weight in a animation curve. When i pressed "free tangent weight" button in Graph, and only got a error message saying "all the animation curves are non-weight. Can't change to free tangent weight mode." What shall i do then? Please give me some help.
Thanx

[alan-1]

I just tried searching but couldn't find a way to change this state once the keys have been made. the setting for this is in under Options > general preferences > then choose the animation tab, look for the 'keys' settings.
alan

[alan-1]

Correction.
go to the graph editor, select your curves, right click, curves > weighted tangents