Via Terminal (ctrl+alt+t) if you don't have them:
sudo apt-get install gksu gedit
Check current swappiness setting via Terminal:
cat /proc/sys/vm/swappiness
(he result will probably be 60)
Open the following text file via Terminal:
gksudo gedit /etc/sysctl.conf
Scroll to the bottom of the text file and add your swappiness parameter to override the default. Copy/paste the following lines:
# Decrease swap usage to a more reasonable level
vm.swappiness=10
(set at 20 or higher if using Dropbox or tray icon will not appear)
Set at 22 if using Dropbox and Skype or Skype icon will appear messed up)
Quicksave, exit and reboot
Check the new swappiness setting via Terminal:
cat /proc/sys/vm/swappiness
(now it should be 10 or whatever you entered above)