How to update theme from ThemeForest?

First you need to install Envato Market plugin. When you first activate the theme you should see a “Install the Envato Market plugin” notice, click on that link to install the plugin. Alternatively you could also download the plugin from here.
Now log in to your WordPress admin dashboard and click on Envato Market on the left sidebar.
Follow the instruction on that page and fill in the required info and click on Save Changes.
Once the page refreshed you should see the list of themes you have purchased.
An update link will appear if there’s new version. Click on that link and your theme will be updated automatically.