Cast-On Edge Question for a Sock

[zanne042]

I have completed a pair of knitted socks in the cuff to toe fashion. Once the sock was presented to the owner it fits well except for the original cast-on edge where the sock began is a bit too tight. Is there a way that I can undo the first or second row and redo the ribbing going up towards the knee instead of the usual down to the ankle? And if so how?
Hopefully it is fixable so I do not need to reknit the entire pair. Any help or advice would be much appreciated.

Thank You !