Leaving should be as easy as arriving.
Standard Windows uninstall. No survey, no “are you sure”, no leftover service.
How to remove it
Settings → Apps → Internet Download Accelerator → Uninstall. Or run the uninstaller from the program folder; both do the same thing.
Browser integration is removed with the program. Extensions installed from a browser's own store have to be removed there — we cannot reach into a browser profile, and you would not want a program that could.
What stays, and why
Your download list, history and settings are left in %APPDATA%\WestByte. That is deliberate: reinstalling after a Windows upgrade should not cost you a queue you spent a week filling.
To remove those too, delete the folder by hand after uninstalling. Downloaded files are never touched.
Export your settings before uninstalling — Export/import of settings — and your list, categories and site manager move with you.