How to Remove the Disk-hogging Sleepimage File from Your Mac | Mac|Life
Swap files are created by OS X when you've exceeded your physical RAM. Don't delete them, as OS X manages them automatically. Restarting your Mac should remove most or all of them, but they will be rebuilt as needed.
To determine if you can benefit from more RAM, launch Activity Monitor and click the System Memory tab at the bottom to check your page outs. Page outs are cumulative since your last restart, so the best way to check is to restart your computer and track page outs under your normal workload (the apps, browser pages and documents you normally would have open). If your page outs are significant (say 1GB or more) under normal use, you may benefit from more RAM. If your page outs are zero or very low during normal use, you probably won't see any performance improvement from adding RAM.
Using Activity Monitor to read System Memory and determine how much RAM is being used