Dark Avatar should update the base game to whatever version it needs it to be at to install.
For the update itself, you will need to use GameStop (formerly Impulse), assuming you had the game registered at least two years or so ago. GameStop won't recognize the retail installation but there is a Detect Application option in GameStop's app that you can use to tell it where it is. Once you do that you should be able to update.
If you didn't register the game before GameStop bought Impulse, or if they've lost your registration and their support can't recover it, you can email our support for an alternate means of updating but it would involve a full download of the game.