How to Reduce the Size of a Thumbnail in WordPress
In this article, we will show you how to reduce the size of a thumbnail image that has already been added to a post.
1) Open the post you wish to edit.
2) Click the image, then click the edit button
3) Click the size percentage you wish to use.
4) Click Update
That’s it! Remember to save your changes to the post by clicking the post’s Update button.