Kemlin,
These instructions are for the Opera Web Browser
When Opera is open if you select > Opera ( Menubar ) > About Opera > it tells you the paths to all its files.
Quit Opera
You can Navigate to these files in the Finder App
Macintosh HD > Applications > Opera
Macintosh HD > Users > My User Name ( This part varies ) > Library ( this is a Hidden folder ) > Application Support > com.operasoftware.Opera
Macintosh HD > Users > My User Name ( This part varies ) > Library ( this is a Hidden folder ) > Caches > com.operasoftware.Opera
If you move the Application, the 2 folders mentioned above, and if you still have it the installer to the trash and then empty it Opera will be uninstalled.
If you have the Opera icon in your Dock you have to remove it manually.
You can remove it by dragging it off the Dock or by ( Right ) ( Clicking ) or ( Control ) ( Clicking ) > select Options > Remove from Dock.
*** Helpful Tip *** In Finder select: Go ( Menubar ) > Hold down the ( Option ) Key on your keyboard > Select Library
This will take you to Your User Library Folder which is hidden by defualt.
You will have to repeat the above steps for each individual user that has open Opera on your Mac.
Also important to note normally it is best to find a uninstaller if you installed an App using a package installer. I search Operas website and couldn't find one. The wiggle and click the X only works for Apps installed through the App Store.
Hope that helps,
Weston