If you really want to delete your account, you'll need to successfully login to Podio. Once you've successfully logged into your Podio account, select the profile icon in the upper right corner of Podio and click "My account", then select "Account Settings" and find the link "I wish to permanently delete my Podio user account". This action is not reversible.
You don't need to delete your account if you no longer want to be part of a workspace - you can just leave the space. To leave a space, click the wrench icon next to the workspace name, then choose "Leave space". You can also click the wrench icon next to the organization name, then choose "Leave organization".