Once you have double-checked that all emails inside the Junk mail folder are spam, and have reported as spam all messages that made it through the Windows Live Hotmail filters and into your inbox, it is time to empty your Junk folder. However, before we go on, let's just mention that Hotmail automatically purges the spam inside the Junk email folder every two weeks or so; in other words, manually deleting junk emails is an optional step, and nothing you actually need to do. Besides, given that Hotmail now offers flexible storage (ever-increasing capacity), spam will not make much difference in your email account space usage and storage needs!
If you want to delete spam from your Hotmail account one screen at a time, you can proceed as follows: (this approach combines the two actions of confirming the spam nature of these emails and deleting them into a single, convenient step).
First, load the spam in your account by clicking on "Junk" in the left hand side:
Once inside the Junk mail folder, go through all visible emails: if one legitimate message was accidentally filtered as spam, just move it to your inbox (by marking it as safe or not). Leave all other messages in there. Then, click on the "Select all" checkbox at the top, and click on the "Delete" button.
All the email messages that were visible in that screen have been deleted, and the next batch will now appear on screen (if any - because the visible emails may have been the entire amount of spam you had in the Junk mail folder at that time).
If you are confident that all emails inside the Hotmail Junk folder are actually spam, you can directly delete all of them; to do so, click on the "Empty" button in the Hotmail toolbar displayed at the top, above the listing of email messages:
You now know how to delete a select group of spam messages in your Hotmail account, and how to completely empty the Junk mail folder in Windows Live Hotmail.com. Which approach you pick is just a matter of personal preference, and how you manage your emails once they are delivered to your account.