if its rounded the as said use an old proppa steel socked and smash it onto the nut......... job done if its too tight., like with most things that are tight need some lub.... give it a good spray with wd40 then hit the top of the nut with a hammer to just free anything that is sticking (the shock of the contact is pretty good for just loosten any rust that may be on there) the get your socket on the end...... stick the rachet on..... then use either a prise bar or a large rind spanner and hook it over the end of your rachet then appliy short hard jerks on it to just loosten it. dont just try pulling with all your might because ull just end up smapping the bolt... try that lol