I'm not a Mint user, but I have used several other Debian and Ubuntu based distros over the last few years. Assuming Mint 13 is based on Ubuntu 12.04 LTS and Mint 14 is based on Ubu 12.10 and assuming Mint isn't too vastly different to Ubuntu under the hood; If anything, it's probably just the release upgrade setting in the software sources options that needs to be set correctly in order to upgrade from 13 to 14.
I can't remember which file you need to edit to set this option from the command line, but if you open the upgrade manager or one of the GUI based package management tools (Software centre, Synaptic etc.. Again, not sure what Mint uses by default) and then go to 'Settings->Configure software sources' to bring up the software sources dialog; then go to the 'Upgrades' tab and set the 'Show new distribution upgrades:' option to 'Normal releases'.
There are two other settings for this option: 'Never' - which means you'll only pick up dist-upgrades for the currently installed version (kernel upgrades etc) and won't get notified when a new version becomes available. 'Long term releases only' - which will only show upgrades when a new LTS version is available.
But setting this option to 'Normal releases' should allow you to pick up any new distribution upgrades.
Once that setting has been made you can either upgrade via the GUI, or you can open a terminal and use: sudo apt-get update && sudo apt-get dist-upgrade And that should start the upgrade to Mint 14!
Like I said, I'm not a Mint user, so I don't know that my instructions are 100% correct. But as Mint is Ubuntu based, I imagine the steps required would be very similar to Ubuntu, if not exactly the same!
Like the above post says, you should @ least be running their latest linux headers and kernel on the previous version if thats all you did.
When you say updated from 13 to 14... Did you do a scripted install over itself? How did you upgrade? Is there any reason you cant just wipe the partition version 13 is on and install version 14 there? Theres no data there right? just the o/s? Complications always bite me when installing overitself.
Personally i keep a goal of constant preparedness to nuke my o/s partition @ any moment and revive without issue. Via running a (well kept & updated & backed up) script after installing the new vesrion, restoring my customizations & i am right back where i was.