Once in a while after you have booked your cruise you may be offered an upgrade on your cabin. This might include a variety of upgrades. Moving to a different location on the ship or getting a higher category of cabin. 

Some upgrades are given free of charge. Not often though.

If you book a guarantee cabin, you have a better chance to get an upgrade on cabin category. This usually comes with an extra charge. 

Other upgrades are offered at a price. 

Some prices are well worth it while some are not. Beware of jumping at an upgrade offer because it might change some of your perks.

Why do cruise lines offer upgrades? Quite often they try to free up space for a group. They also aim to fill random cabins that haven’t been booked. 

In my work as a travel agent I check the cruise line websites regularly to see if there are any upgrades being offered. It’s important to see if my clients can get a good upgrade. If I find one, I immediately contact my client. They typically are first come, first served, and I hate losing it! 

Quite a few cruise lines will let you bid on an upgrade after you book. Carnival has not done it yet.

Hopefully you get an offer one day to consider. But make sure you check the details of the offer. You don’t want to lose any perks you have like onboard credits. Always check with your travel agent before paying for an upgrade.