New Images do not Update on Browser

I get this issue with 2.1.0.2

Sometimes I need to update an image but keep its old name.
When I do that the cache in opencart keeps the old files.

I have cleared the cache directory via ftp but no success.
I also, updated manually the file and upload it inside the cache with appropriate endings i.e 1000x1000 etc and that did not work either!.
I cleared browser's cache that did not work either.

I'm confused, the only thing that works is actually renaming the file but I don't want to do this as I will loose all the google hits
and don't want to create any more re-directs.

How can I go about solving this please?

Thanks.