I have a couple of questions that I am sure have been asked before, so i apolagize in advance

my daughter has steam radiators and only half of the runs are heating up, the rest are cold, she was told to drian the radiators but I have always been told to never drain the radiators. if they need to be drained pls advise how to do this correctly.

also what are the chances of changing the valves to ones that are adjustable without breaking one? they seem to have been on for a long time

thanks for any help