Someone else sending spam using my account

Someone has been sending spam *Removed information for security purposes using my address --there are all these deliveryfailures to all these addresses on my contact list and I tried to send a warning to everyone on my contact list and the same thing happened to me: there's a deliveryfailure, except instead of using my name it says the same thing, that it's from ebayele. I changed my password, but I really don't know what that has to do with resolving the issue I have now :/