Open Overwolf by going to the start menu and searching for Overwolf.
Once Overwolf is open then click the settings cog in the top right of the Overwolf App as highlighted in this image.
Click on About on the left navigation menu.
Click "Development options".
Then click on the "Update extensions now" button.
If there was a new update for the FTB App then after a few minutes, depending on your download speed, you should see the version number next to the FTB App update.
Congratulations you've successfully updated the FTB App!