Hi and welcome back 🙂
You can use some CSS by right-clicking your mouse and opening ‘Inspect’. This YouTube Video is a great visual example. This article on Featured Images is also handy. You’ll always want to use an image with the minimum width requirements to ensure the image isn’t stretched.
I see the image for the ‘Sales Seminar’ event is naturally 300 x 168 and the width of the container for each column is 568 x 326, so 568 pixels should be the minimum width for your event featured images. Unfortunately, most of this falls under theme customization which we’re unable to support. If you need more assistance, check out our list of customizers.
Let me know if any of this helps and best of luck. Cheers!