Launch Opera, and select the Settings option from the sidebar on the lower left.
Scroll down to the Privacy & security panel and click Clear browsing data.
Ensure the box labeled Cached images and files is checked, along with any other browser data you wish to clear. Then, select the time frame you want to erase — to completely clear the cache, select All time — from the drop-down menu. Afterward, click the blue Clear data button in the bottom-right corner.