MyAppStash is an application that runs in the web browser as a toolbar and web extension. You can uninstall it following the steps below:
For Google Chrome and other Chromium-based browsers: type chrome://extensions in the address bar. Press the thrash can icon next to the intended toolbar.
For Firefox: press Shift+Ctrl+A (or open Tools → Add-ons). Press Disable next to the intended toolbar. If you can't find the toolbar in the Extensions tab, switch to the Plugins tab and look there.
For Opera 12.x and older: press Ctrl+Shift+E (or press the Opera button → Extensions → Manage extensions) to open the Extensions menu. Press Uninstall next to the intended toolbar.
In Internet Explorer: open Tools → Manage Add-ons. Select the intended toolbar and press Disable.
After that, try running AdwCleaner to make sure that there are no leftover rogue registry keys or toolbars in your system.