@wyckliffe have you resolved your download issue?
@Toshi Yoshida I always do my upgrades in steps... I hit both the bottom and top of each major release. This is my personal choice. Mainly out of residual fears from ancient versions. Be sure you watch for database updates along the way.
You don't need to unzip and ftp you can use the WordPress plugin upload page it will replace each version.
If you are using gold cart I would disable that until all WPeC updates are complete and then grab the latest version of gold cart.
Test your upgraded store with only store plugins activated and with a default wordpress theme such as 2012 enabled. (be aware you may need to clear the store template cache. You can do this at
SETTINGS > STORE > PRESENTATION Click "Flush Theme Cache"
For good measure I typically also refresh my permalinks along the way a few times as well.
Great that you are testing on a clone first so many people do these upgrades to a fully working LIVE shop... NEVER a good idea. You don't mess with a functional live store ;)