Go too the File menu
-Preferences
-History and cache.
-Click the Two "Clear Buttons"
-Click the "Empty Now" Button
Thats for Opera.
Oi, the manual way.Pick up CCleaner (free, what Kof suggested) and it will clear your cache, empty your recycling bin, delete any temp files not needed, clear firewall logs and a ton more.
It's like owning a vacuum cleaner for your computer.