2 Schools of thought here.
A) If you have a fairly up-to-date system with more than 8GB RAM - Linux will likely never touch the swap unless you are running intensive rendering applications. So, if you meet that standard, I wouldn't sweat the swap partition. I run two boxes with no swap... no problems.
B) Another school of thought is to define a swap partition because, it is a fallback safety valve which, I admit, is always nice to have.
If you adhere to the "B" school of thought, you can use GParted (sudo apt-get install gparted) and CAREFULLY select a partition to be resized.
Then use your mouse to drag the right side of that partitions graphical image to reduce that partition's size... by 2-4GB (or whatever you feel is appropriate)
This creates "unallocated space" which (after applying the above changes) can be defined as a new partition; (again using GParted) which, can be "formatted as" type:SWAP. Apply those changes. et voila! Swap partition.
Another cchool of thought "C" would be to use the swap FILE method detailed in the answer referenced by @mniess above. I've never used that method. So, I do not have any opinion on it.