For the more recent versions, you should have received an email from the developer that contained the following instructions:
This email should have two attachments:
OctaEdit.lic : This is the licence file, copy this to your desktop.
OctaEdit.txt : This is your licence information in a plain text file, so you can copy/paste details easily.
Note: You only need this for v1.1.300 and above.
Copy the OctaEdit.lic file to your desktop.
Launch OctaEdit and click on the OctaEdit logo.
The About form will be displayed. Click the ‘Cog’ button in the bottom right corner.
Enter the below details in the fields; then click the green tick.