Changing wordpress image dimensions
Wordpress automatically resizes images after uploading through the media manager. There are a total of 3 sizes that are saved and these include thumb size, medium size and large size. This effectively means you can choose which size of image you want to show within your pages and articles.
To change the size of the image dimensions you should first be logged in as an Administrator. If you log in as any other role you won't have the permissions that enable you to change the settings.
Once logging in to the wordpress administration area, click on the settings menu tab and then click on media.
From the wordpress media settings page, you can change each image size dimension so you can adjust how your images look within your website.