Yes, don’t think about so much as an upgrade as a “down Price”
You pick the state room you want, and they charge you the price of one category below that, within the parameters given.
Also there must be an available stateroom in that category below, so they know what price to charge you.
Example, you want to book a V2 stateroom. There are no V3 staterooms available, so no upgrade.
so you decide to book a V1 stateroom. There are V2 staterooms available so you will get the V1 for the V2 price.
When it comes to Aqua class, there are only A2 and A1. If there are any A2 available, they will give you an A1 for the A2 price.