I have a cat issue, can anyone help?

My friend's cat is ruining his house. He is having a hard time getting rid of the cat. Today he texted me asking what he should do. I told him to rethink it and he said that he rethought it when he has to replace his upstairs carpet. Then he told me if she should put the cat outside the vet's office in a carrier or a box. Is this a good plan or do you have any more suggestions?