Delete your ProjectAI flightplans from the Flightplans folder and copy and paste the one you have downloaded in it's place - simple! You have to ensure the AC
# number corresponds to the old one to get the correct plane to follow the flightplans. Often the one you download will just have AC
#1. If you are renewing Jet Blue, it might be (example) AC
#3434 to couple a Jet Blue A320 to those flights. Your Aircraft folder will have all your ai aircraft listed, each with its own AC
# number. If you want to connect a new aircraft to existing flightplans (ie one you've downloaded), copy the TITLE of the aircraft from the aircraft cfg file and paste it in place of the old aircraft title, ie
#3434,430,FSPainters A320 JetBlue.
It really is simple when you get the hang of it.