Advice on Walking to help lose weight

[Tillyboo]

I am doing the Paul McKenna System and am hoping to lose 10lbs.
I am walking in the evenings but would like to know how far and how often to optimise my weight loss.
The route I take takes about 30mins and I try to get out at least 3 evenings a week.
Is this enough, should I be walking further/ more often.
I walk at a pace that gets me a little puffed but not gasping ...

Any body with any knowledge on this subject can correct me here, but my gym instructer told me that you should raise your heart rate, but still be able to hold conversation when you have finished (i was running until i couldnt breathe!) because to burn fat your body needs oxygen.Maybe you could get those wrist/ankle weights just to push yourself a little more. Good luck!