From Test-Scratch-Wiki
To remix a project, on the project page click See Inside and edit the project however you want. Then, in the top-right of the project editor, click on the orange Remix to upload the project as a remix from your account.
When uploading a remix, you are prompted to give credit to the original creator of the project in the "Notes and Credits" until something is typed in the box. It is also required that you change an aspect of the project whether it be theme, graphics or scripts. Remember that remixes that do not change anything or do not give credit to the original author can be reported.