The easiest way would be to pick up stitches around the bottom and add length.
You could take out the cast on but you would have to secure a row of stitches above it with a lifeline and then cut and pick out the stitches since it won't unravel easily in that direction.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry