You can get tools to remove a freewheel.
http://www.jensonusa.com/store/product/TL408A00-Shimano+Tl-Fw40+Freewheel+Remover+2Prg.aspx?sc=FRGLUK&cc=GBP
http://www.sidcupcycles.co.uk/productdetails.asp?productid=01171
http://www.tweekscycles.com/Product.do?method=view&n=1131&g=0&p=23044&utm_source=Google&utm_medium=Base&utm_campaign=TweeksCycles
These are the ones that I have used before to remove freewheels before
@lynx started
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You can get tools to remove a freewheel.
http://www.jensonusa.com/store/product/TL408A00-Shimano+Tl-Fw40+Freewheel+Remover+2Prg.aspx?sc=FRGLUK&cc=GBP
http://www.sidcupcycles.co.uk/productdetails.asp?productid=01171
http://www.tweekscycles.com/Product.do?method=view&n=1131&g=0&p=23044&utm_source=Google&utm_medium=Base&utm_campaign=TweeksCycles
These are the ones that I have used before to remove freewheels before