The Trash on a Macintosh is simply a "holding area" for documents that you want to delete. Rather than having one command to delete files and folders on the Mac, Apple has made it a two-step process in order to allow users to recover files that were dragged into the Trash either accidentally or on purpose. But in some instances, there is a problem and files can't be easily deleted from the trash.
Check the Trash Icon
Locate the Trash icon in your dock. If your dock is on the bottom of the screen, then it's on the far right. If it's on one of the sides, then it's the icon closest to the bottom. If there are items in it, the icon will appear "full," like there is crumbled paper in it. If it's empty, it will appear empty. You can click on the Trash icon to view the contents. To remove an item from the Trash, simply drag it onto your desktop or hard drive icon.
Quit and Try Again
Start by quitting out of every application until the Finder is the only item that is open. Then select "Empty Trash..." from under the "Finder" menu in the upper left of the screen. Confirm that you want to continue emptying the trash when the warning appears, and then select the "Empty Trash" button. Allow the process to continue uninterrupted. If you get a warning dialogue box, click on "Continue" to proceed.
Repeat Holding Down the Option Key
Select the "Secure Empty Trash" command from under the "Finder" menu for a more robust way to proceed. This process takes a bit longer than selecting the standard "Empty Trash" method, but is far more effective.
Reboot and Try Again
If you are still unable to fully empty the trash, then reboot your computer and attempt both the "Empty Trash..." and "Secure Empty Trash" commands again. In many instances, powering down/powering up and then attempting to empty the trash works.
The Terminal Solution
If the problem persists, you can use the Terminal program to empty and recreate the Trash for your account, but only if keying in commands doesn't make you squeamish. Open Terminal from within the Utilities (which is found within the Applications folder) and enter the following at the prompt:
sudo rm -rf ~/.Trash
Note that all spaces are single spaces; once you're satisfied that you've keyed in the command correctly, hit the "Return" key. You will now be prompted for your admin password. Once you've entered the password, log out by selecting the "Log Out" command, which is the bottom choice when you pull down on the apple in the upper left corner of the screen. You will need to enter your admin password to log back into your account.