Need Advice changing to Lantus

Hi I have this lady who has her cat on Caninsulin I told her I have everything she needs to change him to Lantus. Freddie is a 10 year old who has been on this stuff for 2 years. He was getting 15 u twice a day. She cut him back to 12 u twice a day she said she is trying to go 12 hours because that is what I did for Trey. He is peeing a lot and is not grooming I told her this could be too much insulin He is a dry food cat so good thing or he would most likely not be here. She does not home test yet but she is willing to give it a try. I told her I had lots of info for her. Just want to know what is the first step we should do . Should she stop the other insulin for a few days while trying to get him on can food. I really want to help but need advice. She is an older lady and don`t have a computer so I said I would ask the question and get her the answer. Ok she is going to call me in the next day or two. So how do we start Thanks so much. I have been with Lantus 4 months he was only on Lantus 2 months and my cat Trey is OTJ for 1 month...If you need more infor please let me know..Kath & Trey