1- Full Installation
2- Upgrade packages:GUI
3- Upgrade packages: apt-cyg
1- Full Installation: graphical interface: downloiad setup-x86_64.exe ( same for the full install)
https://cygwin.com/install.html
it will create a main directy: C:\cygwin64 ( it's a good idea to save setup-x86_64.exe )
2- Upgrade packages
2a- graphical interface: downloiad setup-x86_64.exe ( same for the full install)
https://cygwin.com/install.html
Use the filter to install all the packages ( one by one)
Click on the "Skip" it will change to the release "2.8.7-2" in this case
3- Upgrade packages: apt-cyg ( but first install it 
!!! )
wget https://raw.githubusercontent.com/transcode-open/apt-cyg/master/apt-cyg
>>> apt-get will appear in the directory
Then move it to the bin directory ( /usr/local/bin )
chmod +x apt-cyg
mv apt-cyg /usr/local/bin
Also:
lynx -source rawgit.com/transcode-open/apt-cyg/master/apt-cyg > apt-cyg
install apt-cyg /bin