Previously in Star Citizen, players were quite limited in their ability to perform cross-chasis upgrades for their purchased ship. Most of the time this was limited to either moving to a more expensive variant or shifting between a very limited number of ships. The only other option for those looking to upgrade their ship was to melt their package/ship, potentially losing any goodies that came with it originally.
In a new upgrade to the Star Citizen Pledge Store, it is now possible to upgrade many of the previously released pledge ships. Buying and then applying an upgrade will transform your ship into your chosen model, and will retain any limited items, access passes or insurance levels that came with your original purchase. For example, I could upgrade my Freelancer DUR (Standalone Price: $125.00) into a Constellation Andromeda (Standalone Price: $225.00) for $100. It is only possible to upgrade to a ship of the same price point or higher, with no option to downgrade without melting the package/ship at this time.
If you are interested in taking advantage of this new service, check out the official Star Citizen website.