Attachments Bulk download & reupload

[Cibulo]

Hello, I just switched from phpbb to vb, which I must say is really *amazing*, so far I am totally satisfied for what I've paid.
Anyhow, now I've got an issue, and could be a big one for me.
On my board many people that are not PC experts upload unoptimized images, as heavy as 250kb each. I do not want to prevent them to upload them as they are a great part of my board content and people like that.
When I used phpbb I used to periodically optimize myself all those images, it was a pretty easy task as downloaded a full backup from cpanel, search for the files directory, optimized them with a batch automated process, and then upload again in the same folder overwriting them.
On about 4000 files this saved me more than 300 megs of space in comparison to the original size of the files uploaded by members.

Now, importing to Vb the attachments seemed easy and I can see all of them on my new wb installation.
In the next months people will go on uploading unoptimized attachments which affects both my bandwith and webspace usage.
I logged in via FTP to see the files directory, but there is a strange tree directory, which as far as I have understood reflects folders by userid number, which is split up.
Does this means that now I cannot do anymore what I did before with phpbb?
It would be a big problem for me as I would run out of space for sure in some months
I hope someone will be so polite to help me understand this.