Reduce size of originals?

[Douglas Thompson]

So, our RS has just under 75,000 files. As you can probably image the "originals" (even though they've been resized down to 4000 pixels on their longest dimensions for the most part) are taking up a bunch of disk space.

In talking with our designers and doing some experimenting, we've determined that the originals could be resized down further to 3000 pixels on their longest dimensions without impacting anything much at all.

The problem being that I'm not finding a way to do that en masse. Is there one (short of replacing each one individually which would be tedious at best)?