How to resize all images on wordpress?

We migrated from our wordpress.com site to self-hosted wordpress platform. When we were at wordpress.com our images automatically resized to the max width set by our original blog, so we uploaded various sizes, trusting the program to auto fit them to our column. After migration, because our new column width is now 619 pixels wide, and because our developers neglected to include our instructions to auto resize images, all of our old posts have images in various sizes – many of which are smaller than our current column.

We want all of our images in all of our posts to be automatically resized to the new 619 width. Many of the automatic resize plugins set a max width to help with downsizing, but they don’t seem to have the capacity to for increasing image sizes, which is mainly what we need. Are there any plug-ins that can fix our issue? Or, if editing CSS is the trick, does anyone know the specific code and where it needs to be inserted?