standalone upgrade from older version to current version osx
You could get the installer from wherever you have a decent connection, and then create a USB key with the installer.

Once you have downloaded the installer on any machine, see the quick instructions here: 


  Create a single GPT (GUID) partition on the USB key, and format it.
  Then run:

sudo "/Applications/Install OS X Mavericks.app/Contents/Resources/createinstallmedia" --volume /Volumes/untitled --applicationpath "/Applications/Install OS X Mavericks.app" --nointeraction

  
  "/Volumes/untitled" is the mount point of your USB key. For the
  verbose version with pictures, see here.