How to delete old emails to lower quota

I am reaching the limit on my email quota. I have erased nearly all of my emails, emptied out the trash box and sent box, and my email quota is still at 422 MB. It shows an email count of over 3000 emails. I would like to delete everything that is stored on the server, but can't seem to find an option for that. I previously used an old version of Outlook with windows XP, and have upgraded to Windows 10. I now use the homestead webmail program to view, retrieve, and send my emails. I have no way of accessing the old version of Outlook to delete from there. What do I need to do. I don't want to just upgrade my quota limit, since that does not solve the original problem.