Editing a nested sequence

I have made a nested sequence and now I need to add a voice over .

I edited one of the sub clips  (clip 1)  

so I clicked down to clip 1.. added the audio and extended the duration of clip 1 to suit the audio.

this worked in clip 1 but  the change in duration was not carried through to the master clip.

when I played the master clip.. clip 1 ran for the original duration..

if I change the duration of a subclip how can this be adopted by the master clip?

thanks

kathy