Many of us have this problem — the function to have single images open larger when clicking on it is not automatically created in the editor. Here are two methods to add a link to make the image open in a new window larger. If you get stuck contact WordPress support for help.

Easy way to make a single image open larger in the new WP editor:

1. Upload an image, or a series of images as single images, (I make mine 1200 px on the wide side) and insert it/them into your post or select an exiting image while in edit mode then
2. Click on the Insert/edit Link button (looks a little like a figure 8)
3. Put a check in Open link in a new window/tab and
4. Click Save.
5. Update your post.

A slow way to make a single image open larger in WP Admin:

1. Go to WP Admin
2. Select Posts and
3. Select the post you want to edit
4. Click edit
5. Select the image and then
6. Click on the pencil icon that pops up at the top of the image
7. In the image details window go to display settings and
8. Select full size, and link to media file (this method can also be used to link to a page in your bog or somewhere else).
9. Click Update.
10. Update your post

I think it would be nice if WordPress applied these settings automatically on single image.

Example: