Large-scale asset replacement

Hi,

Soon I am going to be replacing all of the product photos for a Perch Shop (the range is getting professionally photographed). The product images that are being replaced are not used elsewhere on the site. Ideally I would like these to be removed from the server when they are replaced in Perch, otherwise we will end up using a lot of storage space to keep them.

Is there a way of adjusting the buffer for asset clearance so these old images are removed when they are replaced? Currently I am looking at deleting them manually but there are a few thousand so i would rather not have to!

Or is there a way of doing a forced removal of unused assets?

Thanks

Mike