How to delete or deactivate apex class / trigger in Salesforce Production Org?
Unfortunately, it is not as simple as going to the Apex class and hitting the delete button or unchecking the ‘Active’ checkbox. Here are a couple of options that you can choose from
http://www.asagarwal.com/2360/how-to-delete-or-deactivate-apex-class-trigger-in-salesforce-production-org