Upgrade from 10.9.5 to 10.10.* without App Store
Get someone to download the installer from the App Store - just download it, don't install.

Apple documents how to create a bootable installer - https://support.apple.com/en-us/HT201372 using any USB drive or even an SD card should your Mac have that slot.


Plug that device in to your Mac.
Remember to hold down the option key when your Mac starts up.  
Select the device.


One last thing, make sure you check your backup before installing. Time Machine is best. The upgrade isn't designed to have problems, but you never know.