How to use dropna in Pandas?

column_names = ['id','Clump_Thickness','Cell_Size','Cell_Shape','Marginal_Adhesion',
                'Epithelial_Cell_Size','Bare_Nuclei','Bland_Chromatin','Normal_Nucleoli','Mitoses','Class']   

dataset = pd.read_csv(path, names=column_names,
                      na_values = "?", comment='\t',
                      sep=",", skipinitialspace=True)

dataset=dataset.dropna()
dataset=dataset.drop(columns=['id'])