A:AnswerThe drum is what holds the toner cartridge in the printer. It's the black thing that the cartridge sets in. You will need to pull each one out, then remove the toner cartridge and install it into a new drum. Each color needs one. After doing so you will need to reset the drum life counter on the machine. The link below will help you step by step.
http://support.brother.com/g/b/faqend.aspx?c=us&lang=en&prod=mfc9130cw_us&faqid=faq00000154_057