You can change your contact details via the Easybell customer portal. To do this, simply go to "My data" in the customer portal and then click on "Personal data". Uto view or change certain data, move the mouse cursor over the corresponding entry. Then click on the cogwheel symbol to open a pop-up with the data. You can change these. To save changes, click on the orange "Apply" button. 

If you have any difficulties logging into the portal, you can find more information here.