To change the email of a Contact, hover your mouse over the Manage button in the header menu.
A drop down list will appear.
By selecting the option "Contacts", a new page will open up with a list of all the Contacts of your Company.
On the very right hand side of each Contact, are three vertical dots. Once you select these dots, you are given the option to either edit or delete the Contact.
Select "Edit" to edit the Contact.
A new screen will appear. On the top of this new page there is a field where appears the email you want to replace.
Complete the field with the email you want to add.
Once completed, click the "Update this contact" button to complete the request.