CVS--Concurrent Versions System v1.12.12.1: CVS Security and Backup

Hi I need to lock a file using Wincvs. B'z we have a team of 15 developers but all need to update a common files for some changes. any one hlep me how to lock a file so that one developer can edit and commit the file at a time so that Wincvs can not stop other developer editing the same file at the same time when they do cvs update. (pl give some examples if possible)