[seatac76]

Agree with others just take the train to Tokyo Station or Shinigawa station. If it’s your first time just remember to exit on the gate that is staffed because gate adjustments can get tricky. The ticket I selected at NRT was apparently not enough money, as expected they were super helpful and nice about it though.

[tanjtanjtanj]

There are also fare adjustment machines, you put your ticket in and it tells you what difference to pay to "upgrade" your ticket.

Many travelers will just grab a ticket that sounds vaguely correct and then fare adjust at the end. Grabbing an IC card or one of the apps is the easiest course for virtually everyone though.