How do I tailor flight characteristis of a plane?

I downloaded the Grumman Yankee aa1-a , but can't hardly get it to climb. My full size Grumman climbes at around 750 fpm. I opened the aircraft cfg. in NOTEBOOK to make some changes ,but they wont stick and it does'nt make any difference in the way the plane flys . Any suggestions? Thanks for your time.