Hmm... I'm guessing that screen is what you seen in the app when you try to upgrade? I don't have tickets in my account right now so I can't see that wording. I guess they really mean you can modify the ticket at the latest 14 days after 1st use, and I agree it should say that more clearly. Technically one wouldn't have any valid remaining admissions at 14 days if the ticket had already expired, and the above does state "if no admissions remain, a ticket may not be modified or upgraded."
For example, say I have a 2-day ticket which has a 4-day valid window...
- I use 1 day on the ticket
- then 6 days later try to upgrade
- I no longer have a valid admission remaining on the ticket even if I didn't use the 2nd day because the unused day expired with the ticket expiration date