there are 3 things you will need to do:
1) edit the Users table to add new columns for a the additional profile information. since you will not be collecting this information on the registration page, make sure these new columns are configured to allow null values.
2) Add the new form elements to the profile page.
3) Edit the Update Record server behavior on the profile page. You will need to have Data Assist installed to complete this step. Go to Window -> Server Behaviors.
In the server behaviors list, double click the Update Record server behavior.
On the second page of the wizard, select each of the new Columns in the users table, then click the lightning bolt icon to bind the column top the corresponding form element.