Sometimes it happens that an upgrade fails and you forgot to make backups. It's not the worst thing ever that can happen. And can easily be fixed.
When the upgrade halts, LiteCart will have removed all successfully applied patches. If you browse the folder ~/install/upgrade_patches/ you will see that the first remaining patch (by version number) is the patch that halted. (Caution: In alphabetical listing 2.0.1.sql is listed before before 2.0.sql).
We need to edit that failing patch. Remove all commands that were successfully applied until the halting command. The upgrade window should have provided some clues of which command halted.
After solving the cause of the issue it's time to resume the upgrade. This is done by simply refreshing the page and allowing the browser to issue the form request again.
Hopefully you are back on track again.