ak333 and Cordelli, per usual, gave you excellent advice. There is an upsell desk, and if you used an agent, they may have methods of contacting them. We can't call directly, but they can be contacted

Most upgrade opportunities come within 4-6 weeks in my experience with NCL, though some all the way to sailing date. Can always try a couple times.

The amenities in the Jewel Class suites are worth the upgrades in my opinion, especially with the Courtyard. Not a huge fan of NCL overall, but they have the best suites of the mainstream brands. The "ship within a ship" concept is great, and allows you to enjoy a much higher level of service while still enjoying the entertainment onboard, which is where NCL excels.

Enjoy your cruise!