If you still have the previous code, then you can uninstall the application and install it again. If you don't have the installation package, access the link posted below and continue with the installation. At the end of the installation you will be asked to enter the licence code. Paste it exactly as you have it and the software will be registered.
If the licence key doesn't allow multiple activation, then yes, you need to buy a new code from the developers website.
