A majority of users start using the Kubrick theme, and make modifications as they go along to get the weblog to behave exactly the way they want it to. If you are among these users, then you will have to worry about upgrading without losing the changes you have made to the default theme.
The suggested method for dealing with this is as follows:
1) Copy all the templates and files in the wp-content/themes/default/ folder to a new folder, with a different name. Let’s call it “my-theme”.
2) Modify the style.css file in “my-theme”. Change the second line which says:
Theme Name: Default to read
Theme Name: my-theme
3) Go to the “Presentation” tab in the admin page of your weblog, and select the theme “my-theme” to be the active theme for your weblog.
That’s it! This will prevent your changes from being lost when you upgrade when a newer version of WordPress appears. This is also known to generate a mild amount of self-satisfaction and a sense of achievement at having create a new theme