Launch Opera, click the Menu button in the upper-left corner of the browser window and select the Settings option from the drop-down menu.
Afterward, click the Privacy & security panel located on the left side of the resulting window and click the gray Clear browsing data… button near the top of the Privacy section.
Check the box labeled Cached images and files, 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 the beginning of time — from the drop-down menu. Afterward, click the gray Clear browsing data button in the bottom-right corner.