How can we help my dog lose weight?

ello this tym its about my dog, shes a neopolitan masstif cross dogue de bar dorox - french breed lol, shes over weight 10 years old in april next year and suffers from hip displacia and secondry authoritis, although we give her medication an feed her healthy foods and take her for regular exersize we cant seem to get her to loose weight and if she dosent loose weight fast theres a possobility of he not having legs because of th pressure that goes on them witch makes her hip displacment even worse along with her secondry aurthoritis love to hear about your suggestions thanx tara x x x x

regulate how much food you give the dog every day I had a boxer and fed him only twice a day at the same time and he always had fresh water he was a healthy dog and was in the best shape you could possibley get a dog into