How to update a group of entries

[Bob Wilson]

A table has a group of items that have unique entries for images. But the image is really the same for each group so I need to rename those. So a table entry might look like
table products {
name;
image;
}
and the data would be

name = a1 image - a-1.jpg
name = a2 image - a-2.jpg
name = a3 image - a-3.jpg
name = b4 image - b-4.jpg
name = b5 image - b-5.jpg
name = b6 image - b-6.jpg

I want it to end up being

name = a1 image - a.jpg
name = a2 image - a.jpg
name = a3 image - a.jpg
name = b4 image - b.jpg
name = b5 image - b.jpg
name = b6 image - b.jpg

I was thinking to use the update command but can't see what to put in the set option:
update products set image=??? where image like '%-%.jpg'

If it were just one group, I could just put the image name in it. But there are about 9,000 products so I need something automatic. Would someone please explain how to do this?