How to change camera button app? topic

Hi guys i just somehow side loaded the stock gallery and camera app to my XSP as some of you know i haven't been able to install apps from insufficient storage error so after playing around i managed to get it done via APK. Now when i use the camera button our XP has been blessed with it still opens the stock xperia camera app. is there anyway to change this? i do have a rooted phone
Thanks for putting up with my hail of noobish questions but it is appreciated. Cheers guys