Aeronautical Engineering Help needed

Hello,

I am looking into modifying one of the canard designs like the COZY
MkIV and wanted to know what the best way to ensure that what changes
I am proposing are sound and will result in a craft that will exhibit
similar flight charteristics but with increase in performance (range,
gross weight, acrobatic strength, etc...) Are there any software
programs out there that would assist in the design changes? Any
modelling software to show what affect the changes would have? Thanks!

Marc