If your Gateway has internet access, then you just upgrade ignition, and then click on the “update license” link in the Gateway’s configuration web interface (license section).
If you don’t have internet access on the Gateway, then do an offline unactivation and then an activation.
Now that you’re in the 7-day emergency mode, you’ll need to contact your sales rep and let them know. They’ll grant you an extra activation and you can activate again.