If you already have a WordPress blog and you want to use another theme from MyThemeShop you would have a problem with the thumbnail size as the picture are not having the right format for the new theme dimensions.
The themes from mythemeshop have the proper code to serve the images in the right format, the problem is that the old pictures thumbs have to be regenerated to be used by the theme. If you read the MyThemeShop documentation you would see there that they are asking for a plugin to be installed to do this, but if you are like me and you don’t read the documentation you will search online to find the answer and not too many information exists.
The below steps would help you serve scaled images for MyThemeShop themes and possible for others themes:
Using gtmetrix.com to test the site performance I have found that the Serve Scaled Images scores 0 on my site:
The problem is that if the images doesn’t have the proper dimension it would cause that the big image to be loaded and possible the format to not look good on my site. This has to be fixed.
What you need to do is to install a plugin that would regenerate the thumbnail for your old post into the format needed by the theme. The plugin OTF Regenerate Thumbnails would need to be installed that would take care of the thumbnails regenerate. You just install the plugin and she would take care of the rest.