How can I reduce the size of the Featured image on a posting?

Thank you for your prompt reply. I have found that if I upload a smaller image, the post page image is too blurry since it blows it up so large. Here is my site and if you click on any of the homepage images, you will be able to see how over-sized they are in the individual posts. I would like them to be around the same size that they appear when hovered over on the homepage but don’t know where to go to make that change.
Thank you in advance for any solution.
Info-Booklets.com

Thank you for your response.

I had tried all of the available selections under image size selections for Single Posts. I tried all of them again with the same disappointing results. For example, if I select 150×150 it still blows the image way up but it is all pixelated so I went back to selecting the size uploaded. The image on the post page must be at least 1024×1024 if not larger. When I look at the source file it just shows ‘automatic’ which would indicate that the setting that needs changing is somewhere in a file that needs editing to a specific preferred size or percentage.

Gene

Thank you again for your reply.
I added the code to the area for Customizing additional css
I also checked the setting on Single post options and have it set at: full (original).
(I even tried 300×300 but that also did nothing even after clearing my cached files)

The original ebook covers that I upload are always 550×630
They are still exploding way above that size when viewed on the single post
I don’t see anywhere here where it allows me to attach a screenshot or I would include them.

Again, you can view the post images on my site and see how large they appear compared to the homepage images and the mouse-overs.
Info-Booklets.com

Gene

That is the location where I mentioned earlier that I have added it to with no changes in the results.