How do i locate and remove bleeder pins in radiators and baseboards?

I do Property Preservation for loan companies that own houses that are sitting empty. Some companies just want hot water heat systems drained, others are asking to have bleeder pins removed from the baseboards and/or radiators. i'm trying to figure out where to locate these pins and how do i remove them? I have seen the relief valve on top of the boiler, it looks like a valve stem on a tire. Are all the bleeders the same basic thing? Do i need a valve stem remover to remove these? thanks for your help in advance.