To change the name displayed for yourself when sending an email, you'll need to modify your display name in your email provider (i.e. Gmail or Outlook). Afterwards, you'll need to log out and log back into Interseller for the changes to render.
Here's some articles from email providers outlining how to change your name with these services:
Google/Gmail
https://support.google.com/accounts/answer/27442?co=GENIE.Platform%3DDesktop&hl=en
Microsoft/Outlook
https://support.office.com/en-us/article/change-the-display-name-that-e-mail-recipients-see-2b53331a-ba2a-4803-88dc-ac9fe376c8a9
Exchange/IMAP
Not possible at this time.