There are two options to do this:
- Login to your sandbox instance
- Uncheck the active checkbox field
- Create an Outbound changeset, deploy it into production
This method can be time consuming since the changeset could take a while before it reaches your production instance.
This option requires you to install the Force.com IDE. Force.com IDE allows you to access most of the meta-data in Salesforce including your Apex code. For example, You can find the Apex Trigger metadata (createOpp.trigger-meta.xml) and change the status to inactive. Once you sync the change in your production, this Apex Trigger will be deactivated.