Steps to Remove or Disable
1. Force.com IDE should be installed.
2. Connect to the Sandbox Instance using the IDE and find the class or trigger that you want to delete.
3. Open the matching .xml file, and change the Status XML tag from Active to Deleted.
4. Or to disable the trigger change it to Inactive.
Note: Apex class Status can only be changed to "Active" or "Deleted," not "Inactive".
5. Save the file.
6. Select the two files (Code and XML) using "Ctrl-click," and then right-click on one of them.
7. Select Force.com | Deploy to server.
8. Provide your credentials for the Production org and follow the steps.