Removing wp generated images

I run a sports club website which has several thousand pictures on it. My hosting however has counted 190,000 files in my uploads folder. I am lead to believe that a lot of these are different sizes of each image generated by wordpress (large, medium, small and thumbnail).
Is there an easy way to remove these?
I know now to set the sizes of these auto-generated sizes to ‘0’ so they are not generated, but how do I remove those that are currently in the folder?