Login to my website (wp-admin says "not found") to edit some text.

Hi,
I would like to login to my website and add my email address on the “Contact-Us” page, but I am unable to do so.

Some background.
The website was designed by some guy I paid about 4 years ago.
I have only recently found out that my email address is not on the ‘contact us’ page (As is it a form that is submitted), but I would like to add it there now.
I have tried to login to my site using “Mydomain.com/wp-admin” But I get redirected to “not found”.
I can login to my CPanel, but I don’t know where the page I wish to edit is.
Can anyone help me?