Hi, 6th Sense,
As long as you're signed into your account here on photosynth.net, visit http://photosynth.net/yoursynths.aspx to see your account's synths.
On that page, you should see the thumbnails and titles of your synths with an 'X' in the upper right hand corner of each one.
When you click the 'X', your synth is permanently deleted, so be careful. If you'd like to make them public, you can use the [Edit Synth] button near the title of your synth (when you're viewing it and signed into your account) to change its visibility, position and size on the map, which photo loads first, etc., etc.
Hopefully that helps. Let me know if you still have problems or questions.