I've written this based on my experience of Bananian which is Debian based.

Deleting Swap File

swapoff /swapfile1

rm -f /swapfile1

Creating Swap File

The parition needs to be created as a swapfile and not ext3, ext4 or something else.

mktemp /dev/sda1

Create a file of 1GB

dd if=/dev/zero of=/swapfile1 bs=512 count=2048
chmod 600 /swapfile1
mkswap /swapfile1
swapon /swapfile1

vi /etc/fstab

Add an entry or change the existing one

/dev/sda1 swap swap defaults 0 0

or

/swapfile1 swap swap defaults 0 0