Open the Trash in the Dock
Click Empty in the upper-right corner of the Trash window
Confirm by clicking Empty Trash
To empty Trash without opening it, Control-click the Trash icon in the Dock
Select Empty Trash
Confirm by clicking Empty Trash
To force empty, hold Option and click Empty in the Trash window
If prompted, enter your administrator password
If files are in use, close the apps using them and try again