There is not much information in your post so I am having to guess a lot of the details!
You chose Movie Studio as your software, but which version? If it is 17 or earlier this is the wrong forum for you. Please see this post.
If it is version 18 or later you need to go to your Magix account, log in, go to My products, find the listing for the software you ahve and deactivate any registered installation you no longer need.
Allow a few minutes for the change to take effect then try again to activate your software.