A Note about Image Sizes
Huge images can take a long time to load on a web page and can bog the site down in general. Since the web is low-resolution, images don’t need to be large files. For this site about 500 pixels wide is the most you’d need, unless you want viewers to be able to see a large, detailed version of the images.
You can resize an image on your computer before bringing it in if you know how, or there are a few ways to do this in WordPress.
Change the Display Size of an Image
Use this method if you just need a little tweak. This does not reduce the size of the actual file, and WordPress still retains a full-size version of the image. If your file is huge it will still be slow to load.
Option A: Drag a corner of the image.
Option B: Click the image once to select it, and then clicking the pencil icon to edit the settings
On the next screen you can set a “Custom Size”.
Also, setting the “Link to” menu to Media File will allow someone to click on the image and see the full-size version.
To Really Re-size a file
Use this method if you have a huge image and don’t need the full-size version at all.
Click the image once to select it, and then click the pencil icon to edit the settings
Click “Edit Original”
Enter a new width and click “Scale”
For example if you enter 500 pixels wide, the largest version of this image anywhere on the wordpress site will be 500 pixels wide.