The Just Upgrade option means that you will have to send us your turbo, then we perform our modifications on the turbo you provided, and we ship your modified turbo to you.
The Complete Turbo option means that you will not have to send us your turbo, we will source it ourselves, we work on the turbo we provide ourselves and we will send you a modified turbo.
Both options have the same power levels and the same level of modification.