The procedure is quite simple: if possible, uninstall the Plagius from the old computer, this will prevent a possible lock on your activation key.

On the new computer, download the latest version of Plagius and reinstall it, as well as a new installation. Once installed you must insert the same activation key in Plagius. The key validation system will automatically detect the change.

If you can not find your activation key, you can get it back on the site, by the resend activation key in support pane.