Does anyone know how to hack?? I desperately need help!!?

Just yesturday, i sent someone an offline message on yahoo and for personal reasons, i absolutely need to delete it. I swear if i do learn how to hack, i will only do it now to delete my message and would NEVER do it again. It doesnt even have to be hacking, even if you only know how to undo a message or even the email of a yahoo server i could speak to. Please just give me some suggestions. Pleeeaasee!!