There is not straight forward way to do this. The reason is that every field need to be stored in the database and different people want different fields (we have no way of knowing this beforehand).
Adding fields in the profile page needs a bit of PHP and HTML knowledge. If you have that knowledge then you should be able to copy on of the existing fields and add as you need just don’t forget to create the corresponding database table column to store that value (you will need to look at the “eMember_install.php” file for this).