The uninstaller is "installed" when you install the 757. That is why I said to install the 757 (right click on the installer, and select the "Run as administrator" option if available).
After it's installed, go to the Win 10 Start Menu > Captain Sim and right click on the link to uninstall the 757, and select the "Run as administrator" option (if it's available).
Doing that should remove everything to do with the 757, except anything you might have added to it after it's installed (like liveries).

Note. The Windows 10 Start Menu is that square box on the left side of the Task Bar (if the task bar is at the bottom of the screen) - The one that brings up the Tiles.