Ohhh. In the right column of the forum I see “Updating errors”. There it says:
Getting an unauthorized message
When you activate your license, the URL you’re activating it from is authorized on our end.
If that URL changes at any time, you need to re-authorize your license key or you’ll received an “unauthorized” error when trying to update.
To re-authorize your license key, go to Appearance > GeneratePress and click the Save button under your license key field.
I followed the suggestions and my problem is now solved!