I found a post from a while back that should be able to help you lower the resolution on your project. Here is a link to the post: https://answers.unrealengine.com/questions/23023/trouble-configuring-game-settings.html
The answer you would want to follow would the one provided by SRombauts. It prevents you from having to dig around in the ini files.
Let me know if this helps with your issue.
Thanks and have a great day!