To install Lumen on a new computer, first download it from https://lumen-app.com. You can activate the full version using your license key when you first start it up, or anytime later by going to the Lumen menu and choosing Activate Full Version. If your license key is already in use on two computers, you'll have to deactivate one in order to free up an activation.
If you need to locate your license key in your email archives, search for "Paracosm Store" <mailer@fastspring.com> to find the activation email. Or send us a note at support@paracosm.us and we can help you look up your license!
To deactivate Lumen, go to the menu and choose Lumen --> Show License Info --> Deactivate This Computer. Deactivation just means you'll see the watermark once again, and you won't be able to save new patches, but everything else will stay in place. Note that you can activate and/or deactivate Lumen as often as you wish.
You can also transfer any patches you've saved on another computer to a new one by backing them up into a Zip file. In the Browse tab, hold down Shift and click to choose the Patches you want to save. Then right click and choose "Export X Patches". A Zip file will be saved on your desktop. Unzip it on the new computer and then select all the patches and drag them into Lumen. Note that there's no need to transfer the Preset Patches as those come with every Lumen install.