Prevent LiveCD using existing swap partition
If you're using an Ubuntu Live CD, you can disable the use of the swap partition trough the Partition Editor (GParted) by right-clicking the swap partition, and selecting swapoff.
This should allow to to resize the partition.
You can add noswap to the grub parameters to achieve this.
But it's usually easier to let the Live CD boot normally and then in a console type:
sudo swapoff device
Where device is the file or partition of the swap.
If the live CD uses swap you can disable it with swapoff command. Swap is also not required to install Ubuntu, but recommended.