As cygwin doesn’t supply uninstaller, the whole uninstall process should be done manually.
- Stop any service if running.
- Delete cygwin folder. (cygwin)
- Delete cygwin install file folder.
- Delete 2 registry keys.
HKLM\Software\Cygnus Solutions
\HKUS-1-5-21-1801674531-2077806209-2146658873-1004\Software\Cygnus Solutions