Upgrade from 10.9.5 to 10.10.* without App Store I can't open the App Store, and I can't open software update. I've tried all the troubleshooting advice I can find online, but none of it solved my problem, so I figured an OS update was overdue. I'm hoping that will fix it. 

I can't seem to update without the app store, though!
I ran sudo softwareupdate --install —all and restarted (sudo shutdown -r now), but "About this Mac" still tells me I'm on 10.9.5. (Again, clicking the "Software Update" button tries to launch software update, but fails.)
Now, when I run sudo softwareupdate —list it says, "No new software available." 

Is there anything else I can try before I have to take it to the Mac 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.