Tools → Import and Export Settings → Import Selected Environment Settings...
A dialog will appear, prompting you whether or not you want to save your current settings. If you've made extensive customizations and might want to go back to them at a later date, you should choose to save them.
Then click "Next". You'll be prompted to import a set of environment settings. At the top will be the default environment settings options, customized for each language. In your case, you'd choose C#.
If you wanted to re-import your saved settings, you'd do it the same way—just browse to the saved settings file in the final step of the wizard.