This name defaults to the staging name that you initially chose for the site or the live domain that has been applied. You can, however, change the display name of the site. This does not change the staging URL, nor does it affect your live website in any way. The display name is for the my.pressable.com panel only and for your own internal organization.
To change the display name of the site, simply click the edit button while on the single site page. Fill out the modal and submit.