A swap file is a file that contains data retrieved from system memory, or RAM. By transferring data from RAM to a secondary storage device in the form of a swap file, a computer is able to free up memory for other programs [1].
Sometimes, a large swap file can help when your RAM size is limited, e.g., training a large Deep Learning model on your laptop (although it is not a good idea...)
In Linux, we can follow the several steps in the following to change the swap size.
1. disable the current swap file
$ sudo swapoff /swapfile
2. increase (or decrease) the size of swap file (e.g., 8G as below)
$ sudo dd if=/dev/zero of=/swapfile bs=1G count=8
3. Setup the file as our swap file
$ sudo mkswap /swapfile
4. enable swaping
$ sudo swapon /swapfile
5. check the current swap size
$ grep SwapTotal /proc/meminfo
References
[1]. https://techterms.com/definition/swap_file