Resize Image on Item Show Page

The theme I am working with is currently displaying the square thumbnail of my image on the item show page. I would like the image to be larger. I changed the command to draw the full size image, but that is much bigger than necessary and takes up the whole page. Is there a way to create a medium thumbnail and have it display on the item show page?

There is just the "thumbnail" size.

The thumbnail is bigger than the square thumbnail, but smaller than the fullsize.

Also, remember that you can edit the sizes of each of these thumbnail sizes in the Site Settings panel (changing these sizes will affect newly-uploaded files).

Thanks! I was tripped up because I didn't think to reload all the files after changing the settings. Looks great now.