Messenger on the computer?

you wont be able to delete his unless as it will need to be logged in with his pword. To use your own make sure you have a valid yahoo id (you obviously have cos you are using one here lol) then click at the top messenger and sign out. that should sign your son out and give you a log in screen. Just log in with your own details and off you go it is now your messenger and will hold your settings