From your homescreen, menu>settings>applications>manage applications, then choose an app. If the clear cache button is white, it has a cache stored and, obviously, pushing the button will clear it. If you hit clear data, it will erase any settings or information saved for that app.
ok i see now. i guess i was hoping for there to be a universal cache i could clear out in case that has something to do with my phone not updating after the text messages verizon sent me saying the update was sent to my phone.