Assuming you have the latest version, then you are allowed to install on 2 computers. You can check how many free installation slots you have by:
browsing to magix.com
login by clicking the My Account icon
select My Products
Here you will see all your registered product(s), serial number(s) if there is a Show details link this will take you to more information on which computers the software is installed, if it is a currently supported version there will also a download link for it
If you do not have a spare activation slot then you will have to uninstall the program from the old PC and install on to the new PC. Check that you have the installation download before doing this - there will be a download link for it if it is a currently supported version.
Note you will have to download and install all the extras again