Do I need Office 2007 and 2010?

My HP PC came with Microsoft Office Student and Home 2007 pre installed. I subsequently added Office 2010 and bought the activation key which I used. Now when I open some Office docs they use the 2007 version and demand the validation code. I tried the code I bought for 2010 but it doesn't work. Should I uninstall Office 2007? If I do that will my PC just use Office 2010 to open docs?