Updates to Koken themes and plugins are made available through the Koken Store. The Store link in Koken's main navigation will display an alert anytime updates are available for download. When you see an alert, click on Store.
Next click on Updates in the left column.
The main area on the right will display any available updates for themes and plugins you've previously downloaded. Click the Update button next to each update or Update all at the top. Koken will download and install the item(s) automatically.