Download your new Acam.upl file from your support account on the web and save it to a location where you can remember, e.g. Desktop.
When in AlphaCAM V7.5, go to Help and then About, select the show license folder.
You will see two files in the window, delete both files. Exit out of AlphaCAM and go back into it. At this point your lock code will be displayed, select the browse button and point it to your new Acam.upl file.