• 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