Please go to: https://gamefound.com/users/backedprojects#/
Find the project you are interested in, and choose "view orders". 
Then choose the order you want, and click the Action icon. It's the rightmost icon with the three dots, and choose "change shipping".
There you will be able to change your address. 

If that option is not available for you, or you wish to also change your country - please contact us directly.