Image copping/image resize

Helo,

When i upload and set a featured image, it takes the same size as the original on my desktop. Neither WordPress nor my theme crop them to make them all equal in size in my postings and makes them look nice. So sometimes i have a big featured images and sometimes small. Thats not nice at all, it looks messy. So now i have to manually resize them first before i upload, which i dont like.

Is there a plugin that can fix this and gets me steady size featured images in my postings? I tried the ‘Regenarate thumbnail’ plugin, but nothing changed really. My URL is: https://www.stijnspreekt.nl

Thank you!