I guess you need to be a little more specific for any of us to answer your question. Running 4 days a week is enough to HELP you lose weight, yes, if you are burning more calories than you consume. Running is a fantastic cardio exercise, so it burns lots of calories, but if you eat more than you burn, you won't lose weight. I run about 30 miles a week (I run 4 or 5 days and do other exercise as well), but if I don't keep my calorie intake down to a certain amount, I won't lose any weight. So yes, it's a great way to burn calories, but just like with any exercise, it only helps you lose weight if you're making sure the calories you take in aren't higher than the ones you're burning through both exercise and just being alive.
Start by doing what's necessary; then do what's possible; and suddenly you are doing the impossible. -- St. Francis of Assisi