First of all, there's no such thing as 'having to walk'. It is beneficial, and we will encourage you to walk every day, but in the end – it's up to you. 
It depends on the goal in mind. If you want to keep the body healthy and the cardiovascular risk low, aim for about 4 miles a day, or, in other words – 8,000 steps.
If you want to lose weight, you should focus on walking more than you walk now. Walking more will result in burning more calories, which results to you shedding pounds. Good luck! Read more