Modify Code Behind Pages

How do I modify the "code behind" pages? Do I modify them and then redeploy the package? Or, is there an easier way?
That's essentially what you have to do. Modify the code. Rebuild. Repackage.

If you have Visual Studio 2010 Professional (Not sure if lower versions support SharePoint 2010 or not), it should just be a matter of opening the project, making your change, build and then package.