Replace multiple row with sequence value

Hi Folks,I am new to SQL and i have table which has column FULLNAME (Last name, firstname) & USER EMAIL (firstname.lastname@corp.com) and i m looking to replace the value of Fullname like user0001 and User email like user0001@corp.com.In the table total user count is like 1892 with duplicate as well.Need expert help.Regards,Pankaj