How to select all in inbox

[#1]

In the Webmail process supplied by Plusnet I want to select all mail and then delete it. So far I have bot discovered how to Select all the mail
If I select one mail entry and then do a CMD A  it selects all the text in the Mail window.  Then pressing the delete icon only deletes one entry.
I am using Firefox on a Mac.
Thanks for any info
I do not use the Plusnet Mail for real mail as I have my own domain and the PN Mail redirects the real mail to my Google account.

[#2]

Use the first "Select" button underneath the list of emails!

[#3]

Thank you  -
the icons are rather small and feint and not as intuitive as they could be.......
again thanks