GCSE's - How many times?

I am just about to enter my Second year of a college course for a BTEC Extended Diploma in IT. However, when I took my GCSE's in Secondary School, I didn't get the best of results. I didn't have to pay the course fees for my current course, but if I wanted to retake a GCSE course, would I have to pay the fees for that? I'm only 17 so i'm not too sure. Plus, how many times can I retake my GCSE's? Any help would be much appreciated.