speedometer corrections after sprocket change

I have recently went 1 down on the front and two up on the back, with sprockets. I knew that my speedometer would be incorrect but now I am wondering if there is a way of correcting it. I have asked a few people that I ride with and only one of them have ever changed sprocket sizes and he just don't care if his speedometer is correct or not. Is this something I just need to learn to live with or is there a way to correct it? Please someone help me with this issue. Thanks for your time and your help.  

What you need is a device called speedohealer, it hooks into the speed sensor of your bike and allows
you to adjust it based on gear ratio or by %, they are around $110 and be found with a google search. Or you can use a GPS to get your actual speed and calculate the percentage needed for the adjustment. They work well and are available for most bikes. - Corey