Turn off swap:
sudo swapoff -a
Remove or comment out the swap partition entry from /etc/fstab.
Remove the swap partition:
sudo lvremove /dev/mapper/WHATEVER_IT_IS_CALLED--vg-swap
Resize the root partition:
sudo lvresize -l +100%FREE /dev/mapper/WHATEVER_IT_IS_CALLED--vg-root
sudo resize2fs -p /dev/mapper/WHATEVER_IT_IS_CALLED--vg-root
Reboot?