How to customize the Featured Image appearence/position in my Blog Post Page

Hello, I am pretty new in WordPress. Please excuse me if I asked any stupid question. I used “Azera Shop” theme and installed SiteOrigin Plugins (as per instructions from a Video tutorial). While creating a new blog post (using WP Admin->Dashboard->Posts->Add New), I uploaded an image for as “Featured Image”. While displaying the blog page, I find the image appearing big above the new blog entry, spreading from left to right of the post section, just like a page header image.

I want the Featured Image to appear at the left corresponding to each blog posting in a nice small size (say 250 X 250 size).

I tried by all means within my limited capabilities and knowledge in the WP/theme/plugin/widgets world, but failed to do it. Can anyone help me please? Please let me know if I need to provide any specific information.

Thanks in advance.