How can I convert 4wd to awd?

Ok I'm attempting to change my ford escape form 4wd to awd. Someone said it was very possible to do. I was just wondering would it be the best idea. Would it be better having it awd than 4wd. And how do I convert it, I think someone said you just have to add a part because they did it to their truck. I cant remember what it was called. Anyways if you have any information it would be great and if its worth doing. If it helps the weather here is 10 months snow, 2 months not so much snow, so its slippery and roads suck. Anyways let me know please.