• delete a few large message rather than delete a lot of small mails

First, login to webmail (see How to open WebMail on computer)

Select the Junk mailbox, click the mailbox menu on top, select Empty

Do it again for the Trash mailbox

Select Inbox

• Click Options on top

• Sort by Size, Decending

• While holding the Shift or Ctrl, select some biggest messages you want to delete
• click the Delete button

• Do the same for Sent folder
• After deleted messages, empty the Trash folder
• After few minutes (not immediately), notice the free space changed