changing admin email

I have tried several times to change the email address of a wordpress site that I have become responsible for. I cannot contact the previous administrator and have tried to delete his old email address and add one of my own. However, the address will not change because although the site tells me that an email has been sent to the new address, it never arrives. I have tried several times with two different addresses, one a gmail and the other whose address is a site name email.