how to remove an application i downloaded ( mac cleaner ) and how is best to clean my i mac

If there is no uninstaller:

Fixes for Adware and Pop-ups

1. Malwarebytes
2. DetectX 2.11
3. Remove adware that displays pop-up ads and graphics on your Mac
4. Stop pop-up ads and adware in Safari - Apple Support

Basics for Uninstalling Software

Most OS X applications are completely self-contained "packages" that can be uninstalled by simply dragging the application to the Trash. Applications may create preference files that are stored in the /Home/Library/Preferences/ folder. Although they do nothing once you delete the associated application, they do take up some disk space. If you want you can look for them at the above location and delete them, too.

Some applications may install an uninstaller program that can be used to remove the application. If you cannot find the uninstaller then you could download the freeware, Easy Find, to locate files that need to be removed. The places you need to search include:

1. /Home/Library/Applications Support/ folder. Check if the application has created a folder then delete the folder that's in the Applications Support folder.
2. Applications may install a startupitem or a LogIn item. Startupitems are usually installed in the /Library/StartupItems/ folder or the /Home/Library/StartupItems/ folder. Login Items are set in the Users & Groups preferences. Open it in System Preferences, then click on the Login Items tab. Select the item from the list and click on the Delete [-] button to remove it.
3. Some software use startup daemons or agents. Look for them in /Library/LaunchAgents/ and /Library/LaunchDaemons/ or in /Home/Library/LaunchAgents/.

Some applications install a receipt in the /Library/Receipts/ folder. Usually with the same name as the program or the developer. The item generally has a ".pkg" extension. Be sure you also delete this item as some programs use it to determine if it's already installed.

There are many utilities that can uninstall applications. Here is a selection:

1. AppZapper
2. AppDelete
3. Hazel
4. AppCleaner
5. CleanApp
6. iTrash
7. AppBolish
8. AppUninstaller
9. Uninstaller

For more information visit The XLab FAQs and read the FAQ on removing software.

I wrote a free/shareware app to remove junk like this that doesn't require admin rights to install called DetectX:

https://sqwarq.com/detectx/

However, if you want to do it manually (and I don't blame you for not trusting 3rd party apps!), locate and remove the following:

/Applications/Mac Tonic.app

~/Library/Application Support/mtc

~/Library/Application Support/Mac Tonic

~/Library/Mac Tonic

~/Library/LaunchAgents/com.techyutil.tonictasks.plist

If you do it in the Terminal, don't forget to escape any spaces in the file paths.

Disclaimer: this post contains a link to my own website from which I may derive some form of compensation. My website does not contain 3rd party ads.

Try using either EtreCheck or Malwarebytes for Mac to remove it.

Not directly. EtreCheck can help identify where the Mac Tonic components are located. From there you can manually delete them.

No. OS X does not have tools to remove individual third-party installations. It's the user's responsibility to verify new apps and know how to remove them prior to installation.

The best way to "clean up the system" is to erase the drive first. This also means you know what to do to either reinstall Mavericks or to perform an Erase and Install on your model. I cannot tell you more because I don't know the exact iMac model you have, i.e., release date or model ID. The former should be shown in the About This Mac dialog under the Apple menu.