How can a child custody order be changed?

My fiance and I have full custody of his four year old son and have for a little over a year now. In the custody agreement his mother is allowed to have him for one week out of every month in the summer. Well she got her one week with him recently and the hard work we put into potty training him because he was difficult went completely down the drain. He is having accidents two to three times a day and when he was returned to use this weekend after spending time with his mother he smelled of urine and he has a rash on his legs and private area. Is there something we can do to get her time with him knocked down? He goes to her for his week with her the week before schoole starts and I want to be allowed more time with him so the school doesn't have to deal with his accidents. There has got to be something we can do till she can get her act together and take care of him the way she is suppose too.|||You need to explain to her exactly what she needs to do to attempt some consistency. Sorry, but I don't see a child custody order being changed over this. Your problem is with the child, not his mother. Otherwise, you wouldn't have been potty training at 4 years old. I sympathize.|||Take pictures and document everything and then you can hire a lawyer and go back to court. Or call child protective services and talk to them and get them to look into it.