Replacing old AI flightplans with new ones?

Hey guys, just wondering how to change the current flightplans i have for more updates ones that i downloaded off AVSIM libary, think they was made by alpha india.

for example i want to replace the current Singapore Airlines AI flightplan which i downloaded with World of AI with a new singapore AI flightplan from 2011, how do i do this?

thanks in advance

Ryan